Aircraft Fastener Notes

7/27/2019 Aircraft Fastener Notes

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Malaysian Institute of Aviation Technology

Aircraft Fasteners, Bolts, Studs,

Screw and Nuts ,Control Cable


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SPECIFICATIONS AND STANDARDSSpecifications and standards for aircraft hardware are generally identified by

the organization or iginating them.

Some of the common are: AMS Aeronaut ical Material Specif ications AN Air Force-Navy AND Air Force-Navy Design AS Aeronaut ical Standard ASA American Standards Assoc iat ion ASTM American Society for Testing and Mater ial sMS Military StandardNAF Naval Aircraft FactoryNAS National Aerospace StandardSAE Society of Automotive Engineers


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AI RCRA FT HA RDWARE- THREADED FA STENERS -


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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.


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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 threadsFemale threads Male threadsMale threads


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SCREW THREADS condSCREW THREADS TERMINOLOGYThe principal terms used concerning screw threads are as follow:

1. Pitch : The distance from a point on one thread to the correspondingpoint on the next thread.

2. Crest : The prominent point of a thread. The crest diameter is thediameter of the outer circumference of the thread.

3. Root : The bottom of the thread groove.


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SCREW THREADS cond4. Flank : The straight edge which joins the crest and roots.5. 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 deg. for BA(British Association). 60 deg.for UNC (American

Standard Unified Coarse , UNF (AmericanStandard Unified Fine) and metric thread.


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6. Minor diameter The smallest diameter of the thread measured in aplane normal to the axis.

7. Major diameter - The largest diameter of the thread measured in aplane normal to the axis.

8. Effective (pitch) diameter Standard value for a given thread sizeand is appox. Halfway between major and minor

diameter.9. Lead The distance traveled for one revolution of the screw thread.

Lead equals pitch for a single start thread. For multi-startthread lead = pitch x number of start.


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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 threadsbut a strong core diameter. Example; American National series (NF,NC) has more threads per inch

compare to the American Standard Unified Series (UNF,UNC)


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THREAD FORMS

The four common types of thread form are the Vee, Square, Acme, and theButtress.

1. The Vee Thread gives the greatest strength for common usage, such asbolts, and is easily produced by taps and dies2. The square thread stands up well to constant wear and heavy loads ,suchas 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 nut4. The Buttress Thread is used where the thrust is required in one direction only, as withthe bench vice screw.


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The Vee Thread

The square thread

The Acme Thread

The Buttress Thread


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Normally threads are designated by class of fit.

1. Class 1 thread is a loose fit, allow you to turn the nutall the way down using only fingers. Example wing nut

2. Class 2 is a free fit3. Class 3 is a medium fit where screws are typically a

class 2 or 3 fit. Most common aircraft bolts are usuallyfine threaded with a class 3 fit

4. Class 4 is a close fit

5. Class 5 is a tight fit where requires a wrench to turn anut down from start to finish

THREAD TYPE cond

wing nutwing nut


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DESIGNATION CODES

Like rivets, threaded fastener are given a part codeindicating a fastener diameter in 1/16 inch increment and itslength in 1/8 inch increment.

Example AN4-7 identifies a bolt that measures 4/16 or inch in diameter and 7/8 inch in length

AN4-7

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

AIRFORCE-NAVY

AIRFORCE-NAVY

DIA.4/16Or 1/4DIA.4/16Or 1/4

LENGTH.7/8

LENGTH.7/8


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Bolt that is 1 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 inches long.

AN5-22

DESIGNATION CODES cond

AirForce-Navy Diameter5/16in Length -22 = 2in +2/8 or in =2 in


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BOLTSSTANDARD AIRCRAFT BOLT Hold two or more items together Typically used for airframe structural Have hex heads Range from AN3 AN20

Made of cadmium-plated nickel steel, corrosion resistant steel and2024 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


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Holes drilled at the endof the shank Letter A is used

Appears immediately after dashnumber no hole at end of theshank

Absence of A indicates holeexists in the shank

E.g. AN6C 12A Bolt is 3/8 Dia, corrosion

resistant steel, length 1 and undrilled shank .

BOLTS cond


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Propeller boltDrilled through head of the bolt not at the shank

Letter H is used appear after diameter numberE.g. AN6H34A

bolt is 3/8 Dia, nickel steel, drilled head, 3 long andundrilled shank .

Propeller boltDrilled through head of the bolt not at the shank

Letter H is used appear after diameter numberE.g. AN6H34A

bolt is 3/8 Dia, nickel steel, drilled head, 3 long andundrilled shank .


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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


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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


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CLEVIS BOLTS

Range from AN21 AN36 Loaded in shear only

Typically slotted or recessed to accept a screwdriver Installed on forked end


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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


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BOLT SELECTION AND INSTALLATION

J oining 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


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Studs: Types and Uses, Insertion and Removal

Types of Stud

Standard Stud

Waisted Stud

Stepped Stud

Shouldered Stud Fitting Studs


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1. Standard Stud

This is a plain or parallel type.

The diameter of the unthreaded portion is the same as the majordiameter of the screw thread at both end

with the threads merging smoothly into the plain part.


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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.


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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 housingthat, because of damage, has been re-drilled and tapped with a largerdiameter thread.


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4. Shouldered Stud

The projecting shoulder of thisstud gives extra support andresistance to any sidepressure.

How to ins tall Studs

Studs may be inserted by using a stud box and aspanner,

or by fitting locknuts to the stud and using aspanner on the upper nut.


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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


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AN 310 CASTLE NUT Class 3 FIT Made of cadmium-plated nickel steel Corrosion resistant steel 2024 aluminum alloy

Used when the bolt is subjected to either shear or tensile loads


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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 cadmium-

plated nickel steel


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AN316 CHECK NUT Second nut tightened against the primary nut Made of cadmium-plated nickel steel Plain nut is locked in place using a check nut


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AN 340 MACHINE SCREW NUT

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


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AN 345 MACHINE SCREW NUT

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


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AN 355 SLOTTED ENGINE NUT

Use on aircraft engine Made of heat-treated steel

Has national fine threads Class 3 Fit


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AN 360 PLAIN ENGINE NUT

Use on engine only Doesnt have cotter pin slots Has a black rust proof finish


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AN 350 WING NUT Class 2 Fit Made of cadmium-plated steel or brass Has national fine threads

Remove a part frequently without the use of tools


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


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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


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METAL SELF-LOCKING NUT

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


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AN 364 SHEAR SELF-LOCKING NUT

Used in areas that are subject to high temperatures Typically made to be used on clevis bolts that dont have drilled

shanks


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ANCHOR NUT

Permanently mounted nut plates that enable inspection plates and access doors tobe easily removed and installed

Installed around inspection plate openings and installed in a channel that is riveted tothe structure


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TINNERMAN NUTS

Cost economical nuts Commonly used on light aircraft To mount instruments can be either be installed in an instrument panel 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 self-tapping screws.

U - Type


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TORQUE RECOMMENDATIONS

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

used nut and bolt combinations


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SCREWS

Made of lower strength materials typically installed with a loose-fitting thread

The head shape are made to engage a screwdriver or wrench


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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 cadmium plated carbon steel

Round Head Machine- Made of cadmium plated-Available with either fine or coarse thread

Truss Head Machine screw-large head that provide good holding ability on thin

pieces of metal


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STRUCTURAL SCREWS

Made of alloy steel, heat treated & can be used as structuralbolt

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 cadmium 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 cadmium plated high strength steel


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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 Truss head

CountersunkheadCountersunkhead


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PIN

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

removed

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

COTTER P IN- used to safety castellated nut

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


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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


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Locking Washer Provide efficient locking action by spring tension and

biting action of tapered twisted teeth. Made of 1050spring steel and cadmium plated, Class 3. Available withinternal teeth (Type A) or external teeth (Type B)


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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


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HELI- COIL TM 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


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TURNLOCK FASTENERS

Used to repair holes that have been wornoversize or corroded

The hole is drilled oversize and the sleeve ispressed or bonded in place

Then the original fastener is then installed

Turn lock fasteners / quick release fastener Commonly used are the

- DZUS- AIRLOC- CAMLOC

A cr es Sleev e H ole R epa ir


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


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AIRLOC FASTENER

Similar to DZUS fastener


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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.


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Wire LockingSafetying of Nuts, Bolts, and Screws

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 because of vibration.

Safety wiring is the most positive and satisfactory method ofsafetying cap screws, studs, nuts, bolt heads, and turnbucklebarrels that cannot be safetied by any other practicalmeans. It is a method of wiring together two or more unitsin such a manner that any tendency of one to loosen iscounteracted by the tightening of the wire


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TURNBUCKLE SINGLE WRAP


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TURNBUCKLE DOUBLE WRAP


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1. Split Pins

Use with a slotted castellated nut.

Split pins are used once only.

Locking AnD SAFETYing DEvicES


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2. Spring Washers

Supplied as:single coils of square sectionspring with sharp corners or,as double coil of flat spring

Can be re-used if it is still springy andretains it's sharp corners Animation Presentation

Crinkle

washer

Cup

washer


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Double coilSingle coil


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3. Shake Proof Washer

Spring steel washer, which have slantingserration on their internal or external edge


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Shake Proof Washer


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4. Tab Washers

Thin metal washers with two

tabs and a projections.

It is not permissible to

straighten the tab of a tab-washer and re-use it.


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5 . Lock ing Pla te

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.


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6. Circlips These are either spring plate or springwire rings that are spring into grooves.

They may be fitted internally orexternally.

Wire type circlips are use once only.


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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, butit will depend on the size of the wire.


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Wire Safety Installation1

23 4

56 7

89 10


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To prevent nuts frombecoming loose on studs,use castellated nuts and

safety wire themas you would bolt heads.

To prevent nuts frombecoming loose on studs,use castellated nuts and

safety wire themas you would bolt heads.

Aircraft Fastener Notes

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