next slot with the cotter pin hole. The torque loads specified may be used for all unlubricated cadmium-plated steel nuts of the fine- or coarsethread series which have approximately equal number of threads and equal face bearing areas.
These values do not apply where special torque requirements are specified in the maintenance manual.
If the head end, rather than the nut, must be turned in the tightening operation, maximum torque values may be increased by an amount equal to shank friction, provided the latter is first measured by a torque wrench.
AIRCRAFT SCREWS Screws are the most commonly used threaded Torque Tables fastening devices on aircraft. They differ from bolts inasmuch as they are generally made of lower strength materials. They can be installed with a loose-fitting thread, and the head shapes are made to engage a screwdriver or wrench.
Some screws have a clearly defined grip or un- 6-13) : threaded portion while others are threaded along their entire length.
Several types of structural screws differ from the standard structural bolts only in head style.
The material in them is the same, and a definite grip length is provided. The AN525 washer-head screw and the NAS220 through NAS227 series are such screws.
Commonly used screws are classified in three groups: (1) Structural screws which have the same strength as equal size bolts; (2) machine screws, which include the majority of types used for general repair; and (3) self-tapping screws, which are used for attaching lighter parts. A tourth group, drive screws, are not actually screws other damage. but nails. They are driven into metal parts with a mallet or hammer and their heads are not slotted or recessed.
Structural Screws Structural screws are made of alloy steel, are properly heat treated, and can be used as structural bolts. These screws are found in the NAS204 through NAS235 and AN509 and AN525 series.
They have a definite grip and the same shear strength as a bolt of the same size. Shank tolerances are similar to AN hex-head bolts, and the threads are National Fine. Structural screws are available with round, brazier, or countersunk heads. The recessed head screws are driven by either a Phillips or a Reed and Prince screwdriver.
The AN509 (100°) flathead screw is used in 135
countersunk holes where a flush surface is neces- The AN525 washer-head structural screw is used where raised heads are not objectionable.
The washer-head screw provides a large contact area.
Machine Screws Machine screws are usually of the flathead (countersunk), roundhead, or washer-head types.
These screws are general-purpose screws and are available in low-carbon steel, brass, corrosionresistant stees, and aluminum alloy.
Roundhead screws, AN515 and AN520, have either slotted or recessed heads. The AN515 screw has coarse threads and the AN520 has fine Countersunk machine screws are AN505 and AN510 for 82°, and AN507 for 100°.
The AN505 and AN510 correspond to the AN515 and AN520 roundhead in material and usage.
The fillister-head screw, AN500 through AN503, is a general-purpose screw and is used as a capscrew in light mechanisms. This could include attachments of cast aluminum parts such as gearbox cover plates.
The AN500 and AN501 screws are available in low-carbon steel, corrosion-resistant steel, and brass. The AN500 has coarse threads while the AN501 has fine threads. They have no clearly defined grip length. Screws larger than No. 6 have a hole drilled through the head for safetying The AN502 and AN503 fillister-head screws are made of heat-treated alloy steel, have a small grip, and are available in fine and coarse threads.
These screws are used as capscrews where great strength is required. The coarse-threaded screws are commonly used as capscrews in tapped aluminum alloy and magnesium castings because of the softness of the metal.
Self-tapping Screws Machine self-tapping screws are listed as AN504 and AN506. The AN504 screw has a roundhead, and the AN506 is 82° countersunk. These screws are used for attaching removable parts, such as nameplates, to castings and parts in which the screw cuts its own threads.
AN530 and AN531 self-tapping sheet-metal screws, such as the Parker-Kalon Z-type sheetmetal screw, are blunt on the end. They are used in the temporary attachment of sheet metal for riveting, and in the permanent assembly of nonstructural assemblies. Self-tapping screws should not be used to replace standard screws, nuts, bolts, or rivets.
Drive Screws Drive screws, AN535, correspond to the Parker- Kalon U-type. They are plain-head self-tapping screws used as capscrews for attaching nameplates in castings and for sealing drain holes in corrosion proofing tubular structures. They are not intended to be removed after installation.
Identification and Coding The coding system used to identify screws is similar to that used for bolts. There are AN and NAS screws. NAS screws are structural screws.
Part numbers 510, 515, 550, and so on, catalog screws into classes such as roundhead, flathead, washerhead, and so forth. Letters and digits indicate their material composition, length, and thickness. Examples of AN and NAS code numbers follow.
AN501B-416-7 AN = Air Force-Navy standard.
501 = fillister-head, fine thread.
B = brass.
416 - 6-inch diameter.
7 = 16-inch length.
The letter "D" in place of the "B" would indicate that the material is 2017-T aluminum alloy. The letter "C" would designate corrosionresistant steel. An "A" placed before the materia.
code letter would indicate that the head is drilled for safetying.
NAS144DH-22 NAS = National Aircraft Standard.
144 = head style; diameter and thread- 4-28 bolt, internal wrenching.
DH = drilled head.
22 = screw length in 16ths of an inch- 1g inches long.
The basic NAS number identifies the part. The suffix letters and dash numbers separate different sizes, plating material, drilling specifications, etc.
The dash numbers and suffix letters do not have standard meanings. It is necessary to refer to a specific NAS page in the Standards book for the 136
REPAIR OF DAMAGED INTERNAL THREADS Installation or replacement of bolts is simple when compared to the installation or replacement of studs. Bolt heads and nuts are cut in the open, whereas studs are installed into internal threads in a casting or built-up assembly. Damaged threads on bolts or nuts can be seen and only require replacement of the defective part. If internal threads are damaged, two alternatives are apparent: the part may be replaced or the threads repaired or replaced. Correction of the thread problem is usually cheaper and more convenient.
ods of repairing are by replacement bushings or heli-coils.
Replacement Bushings Bushings are usually special material (steel or brass spark plug bushings into aluminum cylinder heads). A material that will resist wear is used where removal and replacement is frequent. The external threads on the bushing are usually coarse.
The bushing is installed, a thread lock compound may or may not be used, and staked to prevent loosening. Many bushings have left-hand threads external and right-hand threads internal.
this installation, removal of the bolt or stud (righthand threads) tends to tighten the bushing.
Bushings for common installations such as spark plugs may be up to .040 oversize (in increments of .005). Original installation and overhaul shop replacements are shrunk fit: a heated cylinder head and a frozen bushing.
Heli-coils are precision formed screw thread coils of 18-8 stainless steel wire having a diamond shaped cross-section (figure 6-14). They form unified coarse or unified fine thread classes 2-band 3B when assembled into (heli-coil) threaded holes.
The assembled insert accommodates UN] (controlled radius root) male threaded members. Each insert has a driving tang with a notch to facilitate removal of the tang after the insert is screwed into a heli-coil tapped hole.
They are used as screw thread bushings. In addition to being used to restore damaged threads, they are used in the original design of missiles, aircraft engines, and all types of mechanical equipment and accessories to protect and strengthen tapped threads in light materials, metals, and plastics, particularly in locations which require frequent assembly and disassembly, and/or where a screw locking action is desired.
FIGURE 6-14. Heli-coil insert.
Heli-Coil Installation Heli-coil installation (figure 6-15) is a 5 to 6 step operation, depending upon how the last step is classed. The following steps are for instructional purposes only. The manufacturer's instructions should be followed during installation.
Step 1: Determine what threads are damaged.
Step 2: (a) New installation of heli-coil, drill out damaged threads to minimum depth specified.
(b) Previously installed heli-coil.
Using proper size extracting tool, place edge of blade in 90° from the edge of the insert. Tap with hammer to seat tool. Turn to left, applying pressure, until insert backs Threads are not damaged if insert is properly removed.
Step 3: Tap. Use the tap of required nominal thread size. The tapping procedure is the same as standard thread tapping.
Tap length must be equal to or exceed the requirement.
Step 4: Gage. Threads may be checked with a heli-coil thread gage.
Step 5: Insert Assembly. Using proper tool, install insert to a depth that puts end of top coil ¼ to ½ turn below the top surface of the tapped hole.
Step 6: Tang break-off.
Select proper break-off tool.
should be removed from all drilled through holes. In blind holes the tangs may be removed when necessary if enough hole depth is provided below the tang of the installed insert.
These are not to be considered specific instructions on heli-coil installation. The manufacturer's instruction must be followed when making an in- Heli-coils are available for the following threads:
unified coarse, unified fine, metric, spark plug and national taper pipe threads.
REPAIR OF DAMAGED HOLES WITH ACRES
FASTENER SLEEVES Acres fastener sleeves are thin wall, tubular, elements with a flared end. The sleeves are installed in holes to accept standard bolts and rivet type fasteners. The existing fastener holes are drilled %4-inch oversize for installation of the sleeves. The sleeves are manufactured in one inch increments. Along their length grooves provide a place to break or cut off excess length to match fastener grip range. The grooves also provide a place to hold adhesive or sealing agents when bonding sleeve into the hole.
Advantages and Limitations The sleeves are used in holes which must be drilled 64-inch oversize to clean up corrosion or other damage. The oversize hole with the sleeve installed allows the use of the original diameter fastener in the repaired hole. The sleeves can be used in areas of high galvanic corrosion where the corrosion must be confined to a readily replaceable part. Oversizing of holes reduces the net cross sectional area of a part and should not be done unless absolutely required.
The manufacturer of the aircraft, aircraft engine or aircraft component should be consulted prior to repair of damaged holes with acres sleeves.
Identification The sleeve is identified by a standard code number (figure 6-16A) which represents the type and style of sleeve, a material code, the fastener shank diameter, surface finish code letter and grip tang for the sleeve. The type and material of the sleeve is represented by the basic code number.
The first dash number represents the diameter of the sleeve for the fastener installed and the second dash represents the grip length of the sleeve. The required length of the sleeve is determined on installation and the excess is broken off of the sleeve. A JK5512A-05N-10 is a 100° low profile head sleeve of aluminum alloy. The diameter is for a 32 inch fastener with no surface finish and is g inch in length.
DRILL. TAP GAGE INSTALL FIGURE 6-15. Heli-coil installation.
ACRES Basic SLEEVE BOLT g) SLEEVE SLEEVE TYPE Part Number PART NO. SIZE LENGTH JK5511 ()04 (X) 100° 509 Tension JK5512( )04 ()() 85516(04 (% 1/8 Head Plus JK5610 K5517()04 () Flange JK5511()45 (X) JK5512 K5516()45 ( #6 Protruding Head (Shear) JK5511 K5517()45 () JK5511()05 (X) 100° Low Profile Head JK5512 JK5512( )05 (X) JK5517()05 (X) JK5516( )05 (X) 5/32 10 JK5511()55 (X) JK5512( )55 (X 100° Standard JK5516()55 ()() #8 10 Profile Head JK5516 JK5517()55 (X) (509 Type) JK5610()55 ()() JK5511()06 (X) JK5512()06 ()) JK5516()06 (X) #10 12 Protruding Head (Tension) JK5517 JK5610()06 ()() JK5511()08 ()) JK5512()08 ()) 100° Oversize JK5516()08 (X) 1/4 16 Tension Head JK5517()08 (X) (1/64 Oversize JK5533 JK5610 08 ( )() Bolt) JK5511()10 ()() 1K5512()10 ( )( ) JK5516()10 (X) 5/16 16 PART NUMBER BREAKDOWN JK5517()10 (X) JK5511 04 N 08 JK5610()10 ( )() "L" at end of part number indicates cetyl alchol lubricant JK5511()12 ()() IK5512()12 (X) Length in sixteenth inch increments. (Required installation length by JK5516()12 (X) K5517()12 ()() 3/8 16 breaking off at proper groove) JK5610()12 (X) | Surface Finish N = No finish ACRES SLEEVE FOR 1/64 OVERSIZE BOLT C = Chemical film per MIL-C-554) SLEEVE PART NO. SIZE BOLT (2) SLEEVE LENGTH Fastener shank diameter in 32nds. K5533(06 ( )) K5533(108 (Y) 13/64 17/64 12 16 Material code JK5533()12 ( )) JK5533()10 (X) 25/24 21/64 16 16
• Basic part number NOTES MATERIAL MATERIAL CODE Acres sleeve, JK5533 1/64 oversize available in A286 steel only.
5052 Aluminum alloy (1/2 hard) 6061 Aluminum alloy (T6 condition) Acres sleeve length in sixteenth inch increments.
A286 Stainless steel (passivate) FIGURE 6-16A. Acres sleeve identification.
HOLE PREPARATION FOR 1/64 OVERSIZE BOLT
BOLT DRILL DRILL SIZE NO. DIA. Existing Fastener 13/64 7/32 0.2187 17/64 9/32 0.2812 21/64 11/32 0.3437 25/64 13/32 0.4062
- Acres Sieeve
HOLE PREPARATION
STANDARD CLOSE FIT FIT 1/64 Oversize Hole BOLT DRILL DRILL DRILL DRILL Structure SIZE NO. DIA. NO DIA.
1/8 9/64 0.1406 28 0.1405 #6 23 0.1540 24 0.1520 5/32 11/64 0.1719 18 0.1695 #8 15 0.1800 16 0.1770 #10 5 0.2055 0.2040 1/4 14 0.2660 17/64 0.2656 5/16 21/64 0.3281 3/8 25/64 0.3908
LINSTALLATION PROCEDURE A. DRILL OUT CORROSION OR DAMAGE TO EXISTING HOLE TO 1/64 OVERSIZE.
B. SELECT PROPER TYPE AND LENGTH
ACRES SLEEVE FOR EXISTING FASTENER ACRES SLEEVE INSTALLATION C. BOND SLEEVE IN STRUCTURE HOLE WITH MIL-S-8802 CLASS A 1/2 SEALANT.
FIGURE 6-16B. Acres sleeve identification.
Hole Preparation See figure 6-16 for drill number for standard or close fit holes. Inspect hole after drilling to assure all corrosion is removed before installing the sleeve. The hole must also be the correct shape and free from burrs. The countersink must be enlarged to receive the flare of the sleeve so the sleeve is flush with the surrounding surface.
Installation After the correct type and diameter sleeve have been selected, use the 6501 sleeve breakoff tool for final installation length. See figure 6-16B for the sleeve breakoff procedure. The sleeve may be installed with or without being bonded in the hole.
When bonding the sleeve in a hole, use MIL-S- 8802A1/2 sealant. Reinstall original size fastener and torque as required.
Sleeve Removal Sleeves not bonded in the hole may be removed by either driving them out with a drift pin of the same diameter as the outside diameter of the sleeve or they may be deformed and removed with a pointed tool. Bonded sleeves may be removed by this method, but care should be used not to damage the structure hole. If this method cannot be used, drill the sleeves out with a drill 0.004 to 0.008 smaller than the installation drill size. The remaining portion of the sleeve after drilling can be removed using a pointed tool and applying an adhesive solvent to the sealant.
Stud Detachable part Stud assembly Grommet Cut-away view of complete Fixed Dzus assembly part spring and Spring assembly rivets FIGURE 6-17. Dzus fastener.
TURNLOCK FASTENERS Turnlock fasteners are used to secure inspection plates, doors, and other removable panels on aircraft. Turnlock fasteners are also referred to by such terms as quick-opening, quick-action, and stressed-panel fasteners. The most desirable feature of these fasteners is that they permit quick and easy removal of access panels for inspection and servicing purposes.
Turnlock fasteners are manufactured and supplied by a number of manufacturers under various trade names. Some of the most commonly used are the Dzus, Camloc, and Airloc.
Dzus Fasteners prevent corrosion. The spring supplies the force that locks or secures the stud in place when two assemblies are joined.
The studs are fabricated from steel and are cadmium plated. They are available in three head styles; wing, flush, and oval. Body diameter, length, and head type may be identified or determined by the markings found on the head of the stud. (See figure 6-18.) The diameter is always measured in sixteenths of an inch. Stud length is measured in hundredths of an inch and is the distance from the head of the stud to the bottom of the spring hole.
A quarter of a turn of the stud (clockwise) locks the fastener. The fastener may be unlocked only by turning the stud counterclockwise. A The Dzus turnlock fastener consists of a stud, DZUS grommet, and receptacle. Figure 6-17 illustrates an installed Dzus fastener and the various parts. 6½ .50 The grommet is made of aluminum or aluminum F - Flush head alloy material. It acts as a holding device for the stud. Grommets can be fabricated from 1100 aluminum tubing, if none are available from normal sources.
The spring is made of steel, cadmium plated to 6½-Body diameter in 16th's of an inch 50 - Length (50/100th's of an inch) FIGURE 6-18. Dzus identification.
sunk, or counterbored hole, depending upon the location and thickness of the material involved.
A quarter turn (clockwise) of the stud locks the fastener. The fastener can be unlocked only by turning the stud counterclockwise.
Airloc Fasteners The Airloc fastener shown in figure 6-20 consists of three parts, a stud, a cross pin, and a stud Stud receptacle. The studs are manufactured from steel assembly and case hardened to prevent excessive wear. The stud hole is reamed for a press fit of the cross pin.
The total amount of material thickness to be secured with the Airloc fastener must be known before the correct length of stud can be selected for installation. The total thickness of material Grommet that each stud will satisfactorily lock together is Receptacle stamped on the head of the stud in thousandths of an inch (.040, .070, .190, etc.). Studs are manufactured in three head styles; flush, oval, and wing.
FIGURE 6-19. Camloc fastener. Installed fastener Dzus key or a specially ground screwdriver locks or unlocks the fastener.
Camloc Fasteners Camloc fasteners are made in a variety of styles and designs. Included among the most commonly used are the 2600, 2700, 40551, and 4002 series in the regular line, and the stressed-panel fastener in the heavy-duty line. The latter is used in stressed panels which carry structural loads.
The Camloc fastener is used to secure aircraft cowlings and fairings. It consists of three parts;
a stud assembly, a grommet, and a receptacle. Stud receptacles Studs Two types of receptacles are available, the rigid type and the floating type. Figure 6-19 illustrates the Camloc fastener.
The stud and grommet are installed in the removable portion; the receptacle is riveted to the Cross pin structure of the aircraft. The stud and grommet are installed in either a plain, dimpled, counter- FIGURE 6-20. Airloc fastener.
1/8 - 3/8 Diameter 7 X 19 7 strands, 19 wires Diameter to each strand 1/16 - 3/32 Diameter 7 × 7 7 strands, 7 wires Diameter to each strand FIGURE 6-21. Cable cross sections.
The cross pin (figure 6-20) is manufactured from chrome-vanadium steel and heat treated to provide maximum strength, wear, and holding power. It should never be used the second time;
once removed from the stud, it should be replaced with a new pin.
Receptacles for Airloc fasteners are manufactured in two types, rigid and floating. Sizes are classified by number-No. 2, No. 5, and No. 7.
They are also classified by the center-to-center distance between the rivet holes of the receptacle:
No. 2, 4 inch; No. 5, 1 inch; and No. 7, 1g inch.
Receptacles are fabricated from high-carbon, heattreated steel. An upper wing assures ejection of the stud when unlocked and enables the cross pin to be held in a locked position between the upper wing, cam, stop, and wing detent, regardless of the tension to which the receptacle is subjected.
CONTROL CABLES Cables are the most widely used linkage in primary flight control systems. Gable-type linkage is also used in engine controls, emergency extension systems for the landing gear, and various other systems throughout the aircraft.
Cable-type linkage has several advantages over the other types. It is strong and light in weight, and its flexibility makes it easy to route through the aircraft. An aircraft cable has a high mechanical efficiency and can be set up without backlash, which is very important for precise control.
Cable linkage also has some disadvantages.
Tension must be adjusted frequently due to stretching and temperature changes.
Aircraft control cables are fabricated from carbon steel or stainless steel.
Cable Construction The basic component of a cable is a wire. The diameter of the wire determines the total diameter of the cable. A number of wires are preformed into a helical or spiral shape and then formed into a strand. These preformed strands are laid around a straight center strand to form a cable.
Cable designations are based on the number of strands and the number of wires in each strand.
The most common aircraft cables are the 7 X 7 and 7 X 19.
The 7 X 7 cable consists of seven strands of seven wires each. Six of these strands are laid around the center strand (see figure 6-21). This is a cable of medium flexibility and is used for trim tab controls, engine controls, and indicator controls.
The 7 X 19 cable is made up of seven strands of 19 wires each. Six of these strands are laid around the center strand (see figure 6-21). This cable is extra flexible and is used in primary control systems and in other places where operation over pulleys is frequent.
Aircraft control cables vary in diameter, ranging 143
from 76 to 8 inch. The diameter is measured as shown in figure 6-21.
Cable Fittings Cables may be equipped with several different types of fittings such as terminals, thimbles, bushings, and shackles.
Terminal fittings are generally of the swaged type. They are available in the threaded end, fork end, eye end, single-shank ball end, and double-shank ball end. The threaded end, fork end, and eye end terminals are used to connect the cable to a turnbuckle, bellcrank, or other linkage in the system. The ball-end terminals are used for attaching cables to quadrants and special connections where space is limited. Figure 6-22 illustrates the various types of terminal fittings.
The thimble, bushing, and shackle fittings may be used in place of some types of terminal fittings when facilities and supplies are limited and immediate replacement of the cable is necessary.
AN663 Double shank ball end terminal AN664 Single shank ball end terminal AN665 Rod end terminal AN666 Threaded cable terminal Turnbuckles A turnbuckle assembly is a mechanical screw device consisting of two threaded terminals and a threaded barrel. Figure 6-23 illustrates a typical turnbuckle assembly.
Turnbuckles are fitted in the cable assembly for the purpose of making minor adjustments in cable length and for adjusting cable tension. One of the terminals has right-hand threads and the other has left-hand threads. The barrel has matching right- and left-hand internal threads. The end of the barrel with the left-hand threads can usually be identified by a groove or knurl around that end of the barrel.
When installing a turnbuckle in a control system, it is necessary to screw both of the terminals an equal number of turns into the barrel. It is also essential that all turnbuckle terminals be screwed into the barrel until not more than three threads are exposed on either side of the turnbuckle barrel.
After a turnbuckle is properly adjusted, it must be safetied. The methods of safetying turnbuckles are discussed later in this chapter.
PUSH-PULL TUBE LINKAGE Push-pull tubes are used as linkage in various types of mechanically operated systems. This AN667 Fork end cable terminal AN688 Eye end cable terminal FIGURE 6-22. Types of terminal fittings.
type linkage eliminates the problem of varying tension and permits the transfer of either compression or tension stress through a single tube.
A push-pull tube assembly consists of a hollow aluminum alloy or steel tube with an adjustable end fitting and a checknut at either end. (See figure 6-24.) The checknuts secure the end fittings after the tube assembly has been adjusted to its correct length. Push-pull tubes are generally made in short lengths to prevent vibration and bending under compression loads.
PINS The three main types of pins used in aircraft structures are the taper pin, flathead pin, and cotter pin. Pins are used in shear applications and 144
Length (Threads flush with ends of barrel) Swaged terminal - Pin eye FIGURE 6-23. Typical turnbuckle assembly.
for safetying. Roll pins are finding increasing uses in aircraft construction.
Taper Pins Plain and threaded taper pins (AN385 and AN386) are used in joints which carry shear loads and where absence of play is essential. The plain taper pin is drilled and usually safetied with wire. The threaded taper pin is used with a taper-pin washer (AN975) and shear nut (safetied with cotter pin) or self-locking nut.
Flathead Pin Commonly called a clevis pin, the flathead pin (MS20392) is used with tie-rod terminals and in secondary controls which are not subject to continuous operation. The pin is customarily installed with the head up so that if the cotter pin fails or works out, the pin will remain in place.
Cotter Pins The AN380 cadmium-plated, low-carbon steel cotter pin is used for safetying bolts, screws, nuts, other pins, and in various applications where such safetying is necessary. The AN381 corrosionresistant steel cotter pin is used in locations where nonmagnetic material is required, or in locations where resistance to corrosion is desired.
Rollpins The rollpin is a pressed-fit pin with chamfered ends. It is tubular in shape and is slotted the full length of the tube. The pin is inserted with hand tools and is compressed as it is driven into place.
Pressure exerted by the roll pin against the hole walls keeps it in place, until deliberately removed with a drift punch or pin punch.
SAFETY METHODS Safetying is the process of securing all aircraft, bolts, nuts, screws, pins, and other fasteners o that they do not work loose due to vibration. A familiarity with the various methods and means of safetying equipment on an aircraft is necessary in order to perform maintenance and inspection.
There are various methods of safetying aircraft parts. The most widely used methods are safety wire, cotter pins, lockwashers, snap-rings, and special nuts, such as self-locking nuts, pal nuts, and jamnuts. Some of these nuts and washers have been previously described in this chapter.
Safety Wiring Safety wiring is the most positive and satisfactory method of safetying capscrews, studs, nuts, boltheads, and turnbuckle barrels which cannot be safetied by any other practical means. It is a method of wiring together two or more units in Self-aligning, anti-friction rod end assembly, adjustable Tube, steel or Clevis, Rod end, Check nut Rod end-threaded aluminum alloy adjustable OUD ОлЮт FIGURE 6-24. Push-pull tube assembly.
6 8 FIGURE 6-25. Safety wiring methods.
such a manner that any tendency of one to loosen is counteracted by the tightening of the wire.
Nuts, Bolts, and Screws Nuts, bolts, and screws are safety wired by the single-wire or double-twist method. The doubletwist method is the most common method of safety wiring. The single-wire method may be used on small screws in a closely spaced closed geometrical pattern, on parts in electrical systems, and in places that are extremely difficult to reach.
Figure 6-25 is an illustration of various methods which are commonly used in safety wiring nuts, bolts, and screws. Careful study of figure 6-25 shows that:
a. Examples 1, 2, and 5 illustrate the proper method of safety wiring bolts, screws, squarehead plugs, and similar parts when wired in pairs.
b. Example 3 illustrates several components wired in series.
c. Example 4 illustrates the proper method of wiring castellated nuts and studs. (Note that there is no loop around the nut.)
d. Examples 6 and 7 illustrate a singlethreaded component wired to a housing or lug.
e. Example 8 illustrates several components in a closely spaced closed geometrical pattern, using a single-wire method.
When drilled-head bolts, screws, or other parts are grouped together, they are more conveniently safety wired to each other in a series rather than individually. The number of nuts, bolts, or screws that may be safety wired together is dependent on the application. For instance, when safetywiring widely spaced bolts by the double-twist method, a group of three should be the maximum number in a series.
When safety-wiring closely spaced bolts, the number that can be safety-wired by a 24-inch length of wire is the maximum in a series. The wire is arranged so that if the bolt or screw begins to loosen, the force applied to the wire is in the tightening direction.
Parts being safety-wired should be torqued to recommend values and the holes aligned before attempting the safetying operation. Never over torque or loosen a torqued nut to align safety wire holes.
Oil Caps, Drain Cocks, and Valves These units are safety wired as shown in figure
6-26. In the case of the oil cap, the wire is anchored to an adjacent fillister head screw.
This system applies to any other unit which must be safety wired individually. Ordinarily, anchorage lips are conveniently located near these individual parts. When such provision is not made, the safety wire is fastened to some adjacent part of the assembly.