Plain Ball seat & socket taper pin AN 960 AC950 & AC955 AN975 Special washers AN 935 Star lock washers FIGURE 6-11. Various types of washers.
in obtaining correct grip length for a bolt and nut assembly. They are used to adjust the position of castellated nuts in respect to drilled cotterr pin holes in bolts. Plain washers should be used under lockwashers to prevent damage to the surface material.
Aluminum and aluminum alloy washers may be used under boltheads or nuts on aluminum alloy or magnesium structures where corrosion caused by dissimilar metals is a factor. When used in this manner, any electric current flow will be between the washer and the steel bolt. However, it is common practice to use a cadmiumplated steel washer under a nut bearing directly against a structure as this washer will resist the cutting action of a nut better than an aluminum alloy washer.
The AN970 steel washer provides a greater bearing area than the AN960 washer and is used on wooden structures under both the head and the nut of a bolt to prevent crushing the surface.
Lockwashers Lockwashers, both the AN935 and AN936, are used with machine screws or bolts where the selflocking or castellated type nut is not appropriate.
The spring action of the washer (AN935) provides enough friction to prevent loosening of the nut from vibration. (These washers are shown in figure 6-11.)
Lockwashers should never be used under the following conditions:
1. With fasteners to primary or secondary structures.
2. With fasteners on any part of the aircraft where failure might result in damage or danger to the aircraft or personnel.
3. Where failure would permit the opening of a joint to the airflow.
4. Where the screw is subject to frequent removal.
5. Where the washers are exposed to the airflow.
6. Where the washers are subject to corrosive conditions.
7. Where the washer is against soft material without a plain washer underneath to prevent gouging the surface.
Shakeproof Lockwashers Shakeproof lockwashers are round washers designed with tabs or lips that are bent upward across the sides of a hex nut or bolt to lock the nut in place. There are various methods of securing the lockwasher to prevent it from turning, such as an external tab bent downward 90° into a small hole in the face of the unit, or an internal tab which fits a keyed bolt.
Shakeproof lockwashers can withstand higher heat than other methods of safetying and can be used under high-vibration conditions safely. They should be used only once because the tabs tend to break when bent a second time.
Special Washers The ball-socket and seat washers, AC950 and AC955, are special washers used where a bolt is installed at an angle to a surface, or where perfect alignment with a surface is required.
These washers are used together. They are shown in figure 6-11.
The NAS143 and MS20002 washers are used for internal wrenching bolts of the NAS144 through NAS158 series. This washer is either plain or countersunk. The countersunk washer (designated as NAS143C and MS20002C) is used 131
to seat the bolt head shank radius, and the plain washer is used under the nut.
INSTALLATION OF NUTS AND BOLTS Bolt and Hole Sizes Slight clearances in boltholes are permissible wherever bolts are used in tension and are not subject to reversal of load. A few of the applications in which clearance of holes may be permitted are in pulley brackets, conduit boxes, lining trim, and miscellaneous supports and brackets.
Boltholes are to be normal to the surface involved to provide full bearing surface for the bolthead and nut and must not be oversized or elongated. A bolt in such a hole will carry none of its shear load until parts have yielded or deformed enough to allow the bearing surface of the oversized hole to contact the bolt. In this respect, remember that bolts do not become swaged to fill up the holes as do rivets.
In cases of oversized or elongated holes in critical members, obtain advice from the aircraft or engine manufacturer before drilling or reaming the hole to take the next larger bolt. Usually, such factors as edge distance, clearance, or load factor must be considered. Oversized or elongated tea or beated e holes in noncritical members can usually be drilled or reamed to the next larger size.
Many boltholes, particularly those in primary connecting elements, have close tolerances. Generally, it is permissible to use the first lettered drill size larger than the normal bolt diameter, except where the AN hexagon bolts are used in lightdrive fit (reamed) applications and where NAS close-tolerance bolts or AN clevis bolts are used.
Light-drive fits for bolts (specified on the repair drawings as .0015-inch maximum clearance between bolt and hole) are required in places where bolts are used in repair, or where they are placed in the original structure.
The fit of holes and bolts cannot be defined in terms of shaft and hole diameters; it is defined in terms of the friction between bolt and hole when sliding the bolt into place. A tight-drive fit, for example, is one in which a sharp blow of a 12- or 14-ounce hammer is required to move the bolt. A bolt that requires a hard blow and sounds tight is considered to fit too tightly. A light-drive fit is one in which a bolt will move when a hammer handle is held against its head and pressed by the weight of the body.
Installation Practices Examine the markings on the bolthead to determine that each bolt is of the correct material.
It is of extreme importance to use like bolts in replacement. In every case, refer to the applicable Maintenance Instructions Manual and Illustrated Parts Breakdown.
Be sure that washers are used under both the heads of bolts and nuts unless their omission is specified. A washer guards against mechanical damage to the material being bolted and prevents corrosion of the structural members. An aluminum alloy washer should be used under the head and nut of a steel bolt securing aluminum alloy or magnesium alloy members. Any corrosion that occurs then attacks the washer rather than the members. Steel washers should be used when joining steel members with steel bolts.
Whenever possible, the bolt should be placed with the head on top or in the forward position.
This positioning tends to prevent the bolt from slipping out if the nut is accidently lost.
Be certain that the bolt grip length is correct.
Grip length is the length of the unthreaded portion of the bolt shank. Generally speaking, the grip length should equal the thickness of the material being bolted together. However, bolts of slighily greater grip length may be used if washers are placed under the nut or the bolthead. In the case of plate nuts, add shims under the plate.
Safetying of Bolts and Nuts It is very important that all bolts or nuts, except the self-locking type, be safetied after installation.
This prevents them from loosening in flight due to vibration. Methods of safetying are discussed later in this chapter.
TORQUE AND TORQUE WRENCHES As the speed of an aircraft increases, each structural member becomes more highly stressed. It is therefore extremely important that each member carry no more and no less than the load for which it was designed. In order to distribute the loads safely throughout a structure, it is necessary that proper torque be applied to all nuts, bolts, studs and screws. Using the proper torque allows the structure to develop its designed strength and greatly reduces the possibility of failure due to fatigue.
Torque Wrenches The three most commonly used torque wrenches are the flexible beam, rigid frame, and the ratchet types (figure 6-12). When using the flexible beam and the rigid frame torque wrenches, the torque value is read visually on a dial or scale mounted on the handle of the wrench.
To use the ratchet type, unlock the grip and adjust the handle to the desired setting on the micrometer type scale, then relock the grip.
Install the required socket or adapter to the square drive of the handle. Place the wrench assembly on the nut or bolt and pull the wrench assembly on the nut or bolt and pull in a clockwise direction with a smooth, steady motion. (A fast or jerky motion will result in an improperly torqued unit.)
When the applied torque reaches the torque value which indicated on the handle setting, the handle will automatically release or "break" and move Basic formula F X L = T F = Applied force L = Lever length betwen centerline of drive and centerline of applied force (F must be 90 degrees to L) T = Torque 90 DEGREES 90 _DEGREES
RATCHET
RIGID FRAME Formula for use with extensions Tw = Te X A A Lever length of wrench B Lever length of wrench plus extension Te Required torque on bolt Tw Torque reading on wrench dial
FLEXIBLE BEAM FIGURE 6-12. Common torque wrenches.
Torque Values in Inch-Pounds for Tightening Nuts On standard bolts, studs, and On bolts, studs, On high-strength screws having a tensile strength and serews having bolts, studs, of 125,000 to 140,000 p.s.i. a tensile strength and screws having of 140,000 to a tensile strength Bolt, Stud 160,000 p.s.i. 160,000 p.s.i.
or Screw Size and over Shear type nuts Tension type nuts (AN320, AN364 and threaded Any nut, Any nut, or equivalent) machine parts except, except (AN-310,A.V365 shear type shear type or equivalent) 8-32 8-36 7-9 12-15 14-17 15-18 10-24 10-32 12-15 20-25 23-30 25-35 1/4-20 25-30 40-50 45-49 50-68 1/4-28 30-40 50-70 60-80 70-90 5/16-18 48-55 80-90 85-117 90-144 5/16-24 60-85 100-140 120-172 140-203 3/8-16 95-110 160-185 173-217 185-248 3/8-24 95-110 160-190 175-271 190-351 7/16-14 140-155 235-255 245-342 255-428 7/16-20 270-300 450-500 475-628 500-756 1/2-13 240-290 400-480 440-636 480-792 1/2-20 290-410 480-690 585-840 690-990 9/16-12 300-420 500-700 600-845 700-990 9/16-18 480-600 800-1,000 900-1.220 1,000-1,440 5/8-11 420-540 700-900 800-1,125 900-1.350 5/8-18 660-780 1,100-1,300 1,200-1,730 1,300-2,160 3/4-10 700-950 1,150-1,600 1,380-1,925 1,600-2,250 3/4-16 1,300-1,500 2,300-2,500 2,400-3,500 2,500-4,500 7/8-9 1,300-1,800 2,200-3,000 2,600-3,570 3,000-4,140 7/8-14 1,500-1,800 2,500-3,000 2,750-4,650 3,000-6,300 1-8 2,200-3,000 3,700-5,000 4,350-5,920 5,000-6,840 I"-14 2,200-3,300 3,700-5,500 4,600-7,250 5,500-9,000 11/8-8 3,300-1,000 5,500-6,500 6,000-8,650) 6,500-10,800 1 1/8-12 3,000-4,200 5,000-7,000 6,000-10,250 7,000-13,500 1 1/4-8 4,000-5,000 6,500-8,000 7,250-11,000 8,000-14,000 1 1/4-12 5,400-6,600 9,000-11,000 10,000-16,750 11,000-22,500 FIGURE 6-13. Standard torque table (inch-pounds).
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.