Aircraft Fastener Notes 152860

Malaysian Institute of Aviation Technology

Aircraft Fasteners, Bolts, Studs, Screw and Nuts ,Control Cable


SPECIFICATIONS AND STANDARDS Specifications and standards for aircraft hardware are generally identified by the organization originating them. Some of the common are: AMS Aeronautical Material Specifications AN Air Force-Navy AND Air Force-Navy Design AS Aeronautical Standard ASA American Standards Association ASTM American Society for Testing and Materials MS Military Standard NAF Naval Aircraft Factory NAS National Aerospace Standard SAE Society of Automotive Engineers


AIRCRAFT HARDWARE - THREADED FASTENERS -


THREADED FASTENERS • Allow parts to be fastened together • Unlike rivet its may be disassembled & reassembled an almost infinite numbers of times. • Include threaded hardware such as bolts, screw and various type of nuts that secure them.


SCREW THREADS • A male (external) screw thread is formed by cutting a helical groove into the surface of a round bar, whilst a female (internal) thread is a helical groove cut in cylindrical hole.

Female threads

Male threads


SCREW THREADS con’d SCREW THREADS TERMINOLOGY The principal used concerning screw threads are as follow: 1. 2. 3.

Pitch: The distance from a point on one thread to the corresponding point on the next thread. Crest: The prominent point of a thread. The crest diameter is the diameter of the outer circumference of the thread. Root : The bottom of the thread groove.


SCREW THREADS con’d 4. 5.

Flank : The straight edge which s the crest and roots. Thread Angle : The angle between the flank. This varies for different type of screw system. e.g. 55 deg. for BSW (British Standard Whitworth) and BSF (British Standard Fine) , 47 ½ deg. for BA (British Association). 60 deg.for UNC (American Standard Unified Coarse , UNF (American Standard Unified Fine) and metric thread.


6. 7. 8.

9.

Minor diameter – The smallest diameter of the thread measured in a plane normal to the axis. Major diameter - The largest diameter of the thread measured in a plane normal to the axis. Effective (pitch) diameter – Standard value for a given thread size and is appox. Halfway between major and minor diameter. Lead – The distance traveled for one revolution of the screw thread. Lead equals pitch for a single start thread. For multi-start thread lead = pitch x number of start.


THREAD TYPE •

•

•

•

Aircraft bolts, screws and nuts are threaded in either coarse thread or fine thread. Coarse thread when there are a few thread per inch and has strong threads but a weak core diameter. Fine thread when there are more thread per inch and has weak threads but a strong core diameter. Example; American National series (NF,NC) has more threads per inch compare to the American Standard Unified Series (UNF,UNC)


THREAD FORMS

The four common types of thread form are the Vee, Square, Acme, and the Buttress. 1. The Vee Thread gives the greatest strength for common usage, such as bolts, and is easily produced by taps and dies 2. The square thread stands up well to constant wear and heavy loads ,such as met with screw jacks. This type of thread is readily cut on a lathe. 3. The Acme Thread is for use on the lead screws of lathes to facilitate the opening and closing of a split nut 4. The Buttress Thread is used where the thrust is required in one direction only, as with the bench vice screw.


The Acme Thread

The square thread

The Buttress Thread

The Vee Thread


THREAD TYPE con’d • Normally threads are designated by class of fit. 1. 2. 3.

4. 5.

Class 1 thread is a loose fit, allow you to turn the nut all the way down using only fingers. Example wing nut Class 2 is a free fit Class 3 is a medium fit where screws are typically a class 2 or 3 fit. Most common aircraft bolts are usually fine threaded with a class 3 fit Class 4 is a close fit Class 5 is a tight fit where requires a wrench to turn a nut down from start to finish wing nut


DESIGNATION CODES •

•

Like rivets, threaded fastener are given a part code indicating a fastener diameter in 1/16 inch increment and its length in 1/8 inch increment. Example AN4-7 identifies a bolt that measures 4/16 or ¼ inch in diameter and 7/8 inch in length AN4-7

AIR FORCE-NAVY •

DIA.4/16 Or 1/4

LENGTH. 7/8

For bolt longer than 7/8 inch, the code changes. E.g 1 inch bolt is identified by a -10 representing 1 inch and no fraction. There are no -8 or -9. Dash numbers go from -7 to -10, from -17 to -20 and from -27 to -30.


DESIGNATION CODES con’d • Bolt that is 1 ½ long is identifies by -14. • Bolt with the code AN5-22 identifies an Air Force-Navy bolt that is 5/16 inch in diameter and 2 ¼ inches long. AN5-22

Air Force-Navy

Diameter 5/16in

Length -22 = 2in + 2/8 or ¼ in = 2 ¼ in


BOLTS STANDARD AIRCRAFT BOLT • • • • •

•

•

Hold two or more items together Typically used for airframe structural Have hex heads Range from AN3 – AN20 Made of cium-plated nickel steel, corrosion resistant steel and 2024 aluminum alloy Corrosion resistant steel bolt is identified by the letter “C” inserted between the diameter and length designations. Whereas aluminum alloy bolt are identified by the letter ‘DD’


BOLTS con’d • Holes drilled at the end of the shank – Letter “A” is used • Appears immediately after dash number – no hole at end of the shank • Absence of “A” – indicates hole exists in the shank • E.g. – AN6C – 12A – Bolt is 3/8” Dia, corrosion resistant steel, length – 1 ¼ “ and undrilled shank.


Propeller bolt Drilled through head of the bolt not at the shank Letter “H” is used appear after diameter number E.g. – AN6H34A bolt is 3/8” Dia, nickel steel, drilled head, 3 ½ “ long and undrilled shank.


DRILLED-HEAD ENGINE BOLTS • • • • •

Range from AN73 –AN81 Hex-headed Have thicker head Drilled with small hole in the center of the head Made with either fine or course threads


CLOSE TOLERANCE BOLTS • • • •

Designated AN173 – AN186 Ground to a tolerance of +0.000 -0.0005 inch Used in areas that pounding loads Triangle mark on their heads


CLEVIS BOLTS • • • •

Range from AN21 – AN36 Loaded in shear only Typically slotted or recessed to accept a screwdriver Installed on forked end


INTERNAL WRENCHING BOLTS • • • •

Range from MS20004 – MS20024 High-strength steel bolts Used primarily in areas that are subjected to high tensile loads Six-sided hole is in the center of head to accept an Allen wrench


BOLT SELECTION AND INSTALLATION • • •

ing two pieces of material Washer must be added if the grip length is slightly longer than thickness Check the installing drawing to be sure the correct hardware when installing the bolt ,washer ,and nut combination


Studs: Types and Uses, Insertion and Removal Waisted Stud Standard Stud

Stepped Stud

Types of Stud

Shouldered Stud

Fitting Studs


1.

Standard Stud This is a plain or parallel type. The diameter of the unthreaded portion is the same as the major diameter of the screw thread at both end 

with the threads merging smoothly into the plain part.


2. Waisted Stud This is a weight-saving stud. The plain shank of the stud is reduced to the minor diameter of the screw thread. 

This will lightening the stud without losing any of its strength.


3. Stepped Stud The purpose of this stud is two fold. First its larger diameter end provides a stronger anchorage  particularly useful when the stud is located in soft metal. Second, it is used as a replacement stud and fitted in a stud housing that, because of damage, has been re-drilled and tapped with a larger diameter thread.


4. Shouldered Stud The projecting shoulder of this stud gives extra and resistance to any side pressure.

How to install Studs Studs may be inserted by using a stud box and a spanner, or by fitting locknuts to the stud and using a spanner on the upper nut.



NUTS • • • • •

Used in aircraft construction to prevent them from loosening and falling off 2 types of nuts Self-locking –- locks onto a bolt on its own Non self-locking --- relies on either a cotter pin ,check nut, or lock washer to hold it in place


AN 310 CASTLE NUT • • • • •

Class 3 FIT Made of cium-plated nickel steel Corrosion resistant steel 2024 aluminum alloy Used when the bolt is subjected to either shear or tensile loads


AN 320 SHEAR CASTLE NUT • Same type as a AN 310 • Thinner than standard • Used only for shear loads on clevis bolts


AN 315 PLAIN NUT • • • •

No castellation Fine thread have no locking provisions A spring –type lock washer used in combination with the nut Corrosion resistant steel, 2024 aluminum alloy, made of ciumplated nickel steel


AN316 CHECK NUT • • •

Second nut tightened against the primary nut Made of cium-plated nickel steel Plain nut is locked in place using a check nut


AN 340 MACHINE SCREW NUT • • • •

Have coarse threads Available in carbon steel Corrosion resistant steel Brass and 2024 aluminum alloy


AN 345 MACHINE SCREW NUT • • • •

Have national- fine series threads Corrosion resistant steel Made of cium-plated carbon steel Commercial brass and 2024 aluminum alloy


AN 355 SLOTTED ENGINE NUT • • • •

Use on aircraft engine Made of heat-treated steel Has national fine threads Class 3 Fit


AN 360 PLAIN ENGINE NUT

• Use on engine only • Doesn’t have cotter pin slots • Has a black rust proof finish


AN 350 WING NUT • • • •

Class 2 Fit Made of cium-plated steel or brass Has national fine threads Remove a part frequently without the use of tools


SELF- LOCKING NUT • Design to keep them from coming loose • 2 general type – the fiber or nylon type / all metal type


LOW- TEMPERATURE SELF LOCKING NUTS • • • • •

AN365 Used on bolts and machine screw Held in position by nylon insert above the threads Class 3 Fit nut allows it to rundown on bolts threads easily until the bolt enters the insert Limited to operating temperature below 250 F


METAL SELF-LOCKING NUT • • •

Usuable to 250 F ( 121 C) Made of corrosion resistant steel Available in either NF or NC threads


AN 364 SHEAR SELF-LOCKING NUT • •

Used in areas that are subject to high temperatures Typically made to be used on clevis bolts that don’t have drilled shanks


ANCHOR NUT • •

Permanently mounted nut plates that enable inspection plates and access doors to be easily removed and installed Installed around inspection plate openings and installed in a channel that is riveted to the structure


TINNERMAN NUTS • • • • •

Cost – economical nuts Commonly used on light aircraft To mount instruments can be either be installed in an instrument or in the instrument case itself To reduce the chance of magnetic interference To protect aircraft skin from damage by repeated insertion and removal of selftapping screws.

U - Type



TORQUE RECOMMENDATIONS • •

To ensure preloading is accomplished Give recommended minimum and maximum torque values for the most commonly used nut and bolt combinations


SCREWS • •

Made of lower strength materials typically installed with a loosefitting thread The head shape are made to engage a screwdriver or wrench


MACHINE SCREWS •

Which are the most widely used – –

• •

Fairing, inspection plates, fluid line clamps, light structural part Fully threaded shank

Class 2 or free fit National fine threads  Fillister-Head Machine Screw -Class 3 fit -(MS 35265) coarse thread -(MS 35266) fine thread  Flat-Head Machine Screw -Countersunk Screw -Made of cium plated carbon steel  Round – Head Machine - Made of cium plated -Available with either fine or coarse thread  Truss – Head Machine screw -large head that provide good holding ability on thin pieces of metal


STRUCTURAL SCREWS •

Made of alloy steel, heat treated & can be used as structural bolt – –

•

•

•

Strength equal to bolt at the same size NF standard thread

Fillister – Head Screw - the cross on its head indicating that it is made of high – strength steel - fine or coarse thread Flat – Head Screw - made of heat – treated carbon steel - distinguished from 100 degree by the “ X “ marked on their head to increase the screw holding ability - Made of cium plated high-strength steel Washer head screw – – – –

Washer form onto their head Increase screw holding ability Used on thin area (thinner sheet metal plate) Made of cium plated high strength steel


SELF TAPPING SCREWS • •

TYPE A – has a gimlet ( sharp ) point TYPE B – has a blunt print with threads 4 type of head - Round Head - Countersunk Oval Head - Truss Head - 100 degree Countersunk Head

Truss head

Countersunk head


PIN •

ROLL PIN - used to provide a pivot for t where the pin is not likely to be removed

•

CELVIS PIN - used for hinge pins in some aircraft control systems

•

COTTER PIN - used to safety castellated nut

•

TAPER PIN - produce a tight fit in a reamed hole for applications in shear


WASHER • • • •

Provide a bearing surface area for nut Act as spacer or shims to obtain the proper grip length for a bolt To prevent the nut from vibrating loose 3 most common types of used in airframe - Plain Washer - Lock Washer - Special Washer • •

Finishing washer Keyed washer


Locking Washer • Provide efficient locking action by spring tension and biting action of tapered twisted teeth. Made of 1050 spring steel and cium plated, Class 3. Available with internal teeth (Type A) or external teeth (Type B)


HOLE REPAIR HARDWARE • •

Threaded holes wear out after repeated insertion and extraction of fastener Hole repair hardware allows to make a fast and inexpensive repair to worn or the damage holes


HELI- COILTM INSERT • • • •

Typically consist of a helix of stainless steel having a diamond cross section Typically installed in soft casting when the component is manufactured When are used in a repair, the repair must be approved by the component manufacturer or by the FAA Thread Repair Using a TIME-SERT Insert.flv


Acres Sleeve Hole Repair • • •

Used to repair holes that have been worn oversize or corroded The hole is drilled oversize and the sleeve is pressed or bonded in place Then the original TURNLOCK fastener is then installed FASTENERS

• Turn lock fasteners / quick release fastener – Commonly used are the

- DZUS - AIRLOC - CAMLOC


DZUS FASTENERS •

Cowling and other inspection access doors that frequently open put this fastener.


AIRLOC FASTENER •

Similar to DZUS fastener


CAMLOCK FASTENER • •

the stud assembly of a Camlock fastener consists of a housing containing a spring and a stud with a steel pin Held onto the removable portion of the cowling or access door with a metal grommet.



Wire Locking Safetying of Nuts, Bolts, and Screws It is very important that all bolts or nuts, except the selflocking type, be safetied after installation. This prevents them from loosening in flight because of vibration.

Safety wiring is the most positive and satisfactory method of safetying cap screws, studs, nuts, bolt heads, and turnbuckle barrels that cannot be safetied by any other practical means. It is a method of wiring together two or more units in such a manner that any tendency of one to loosen is counteracted by the tightening of the wire


Corrosion resisting steel and heat resisting nickel alloy are the materials normally used in the wire recommended for wire locking. The following techniques are equally effective: 1. Double twisted method. 2. Single strand with 2.5 twists at originating end and closing end.



TURNBUCKLE SINGLE WRAP


TURNBUCKLE DOUBLE WRAP


Locking AnD SAFETYing DEvicES 1. Split Pins 

Use with a slotted castellated nut.



Split pins are used once only.


2. Spring Washers Supplied as:  single coils of square section spring with sharp corners or,  as double coil of flat spring Can be re-used if it is still springy and retains it's sharp corners

Animation Presentation

Crinkle

Cup

washer

washer


Single coil

Double coil


3. Shake Proof Washer Spring steel washer, which have slanting serration on their internal or external edge


Shake Proof Washer


4. Tab Washers Thin metal washers with two tabs and a projections. It is not permissible to straighten the tab of a tabwasher and re-use it.


5. Locking Plate A thin metal plates, fitted around the nut or bolt after it has been fully tightened. Can be re-use provided they are still a good fit on the nut or bolt.


6. Circlips These are either spring plate or spring wire rings that are spring into grooves. They may be fitted internally or externally. Wire type circlips are use once only.


Safety Wire or wirelock Safety wire is available in a variety of gauges and materials, depending on the application. In aircraft applications, stainless steel wire is used, most commonly in 0.032 in (0.81 mm) diameter. It must be installed in the locking direction of the bolt. Generally the amount of twist is around 6-8 twist per inch, but it will depend on the size of the wire.


Wire Safety Installation 1 2

4

3

5 6

8

7

9 10


To prevent nuts from becoming loose on studs, use castellated nuts and safety wire them as you would bolt heads.

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