Aircraft Hardware: Wedges and Screws

Knowledge Levels

• Basic knowledge for categories A, B1, and B2 is indicated by knowledge levels 1, 2, or 3; Category C applicants must meet either the B1 or B2 basic knowledge level.
• Level 1 includes basic elements of the subject, simple descriptions using common words, and typical terms.
• Level 2 includes general theoretical and practical knowledge, ability to apply knowledge, understanding the fundamentals, use mathematical formulae and understanding sketches.
• Level 3 requires detailed theoretical and practical knowledge, capacity to combine knowledge logically, understanding of interrelationships, application of knowledge via manufacturer's instructions and interpretation of results.

Aircraft Hardware

• A wedge, a simple machine, applies load based on its inclination; steeper wedges move greater distances, shallower wedges raise greater weight.
• A screw, considered an inclined plane wrapped around a cylinder, with the "pitch" (P) being the distance along the cylinder per full helix turn.
• Shallow wedge angles create fine pitch threads, while steeper angles create coarse pitch threads.
• More force can be exerted between the surfaces of a shallow wedge than when the wedge angle is greater.
• Shallow wedge angles produce more considerable friction, resulting in an increased resistance to loosening, which is desirable for threaded fasteners.
• Greater travel (P) will be produced by a coarse thread when a thread is used to produce motion.

Screw Terminology

• Pitch is the distance from any point on a screw thread to the equivalent point on the next thread, measured parallel to the axis.
• Pitch is equal to 1 thread per square inch.
• Effective diameter is also called the pitch diameter and is the diameter of an imaginary cylinder which splits the fundamental triangles exactly in half.
• Minor diameter is the distance between the roots of a male thread and between the crests of a female thread.
• Major diameter is the measured diameter over the crests of the thread or roots in the female.
• Crest is the top surface that joins the flanks of the thread.
• Root is the bottom of the groove joining adjacent sides or flanks of the thread, whether of the male screw or of the female screw.
• Flank or Side is the surface of the thread form connecting the crest to the root.
• Thread Angle is the included angle between the flanks and measured in the axial plane.
• Lead is the axial distance a screw thread advances in one complete turn and is equivalent to pitch for a single start thread.
• Length of Engagement is the axial distance over which two mating threads make contact.
• Angular Depth is a triangle formed by the intersection of extended flanks in which the vertical height of this triangle is the angular depth.
• Actual Depth is the linear distance between the crest and the root of the thread and measured perpendicular to the axis.
• The Fundamental Triangle is the triangle formed by the intersection of the extended flanks (XYZ).
• Truncation is the distance measured radially from the crest or root of the thread to the adjacent apex of the fundamental triangle.

Screws and Threads

• Aircraft hardware consists of fasteners and small items necessary to manufacture or repair an aircraft.
• Safe and efficient operation requires correct selection/use of aircraft hardware.
• Vibration is always present during aircraft operation so provision must be made for safely tying or locking fasteners.
• Aircraft hardware is identified by originating organization, engineering data, materials and processes.

Thread Callout

• Thread callout example: 3/8" 16 UNC.
• External diameter of thread is 3/8".
• Number of threads per inch (TPI) is 16.
• The thread form is Unified National Coarse (UNC).

Aircraft Hardware Standards

• Standards ensure hardware specifications within the aircraft industry.
• American Standards: AN (Airforce Navy), MS (Military Standard), NAS (National Aerospace Standards.)
• European or French Standards: NSA (NATO Standardisation Agency).
• Aircraft Manufacturers' Standards: BAC (Boeing Aircraft Corporation), FON (Fokker), AMS (Aeronautical Materials Specifications).
• Standard hardware available from aviation suppliers has a specification number.
• Special fasteners must be replaced with same part number.
• Variation between standard and special is the material, tolerance, or inspection.
• AN fasteners are replaceable by NAS and MS equivalent fasteners, however NAS and MS hardware must not be replaced by AN hardware.

Bolts and Screws

• Fastening devices allow quick dismantling of aircraft parts at frequent intervals.
• Bolts and screws provide security and rigidity.
• Bolts are used when great strength is required, screws are for when strength is not the deciding factor.
• Bolts have a blunt, threaded end while a screw can be either blunt or pointed.
• A bolt typically uses a nut.
• A screw may fit into a female receptacle or directly into the material.
• Bolts have a short thread section with a long grip length.
• Screws have a longer thread and may have a defined grip length.
• Bolts are tightened by the nut with the head optionally designed for turning.
• Screws are always tightened by turning the screw head.
• Replace aircraft fasteners with duplicates of the originals.

Thread Classification

• Single thread is one continuous groove, used for adjustment and fastening, having a lead that equals the pitch.
• Multiple start threads consist of two or more ridges left by grooves cut side by side.
• Axial travel or lead is increased without changing the pitch; lead equals pitch multiplied by the number of starts.
• Right hand thread tightens clockwise.
• Left hand thread tightens counter clockwise, only used for special purposes.

American Standard Threads

• ANC - American National Coarse
• ANF - American National Fine
• ANEF - American National Extra Fine
• ANP - American National Pipe

Unified Standard Threads

• UNC - Unified National Coarse
• UNF - Unified National Fine
• UNEF - Unified National Extra Fine

British Standard Threads

• BSW - British Standard Whitworth
• BSB - British Standard Brass
• BSP - British Standard Pipe
• BSPT - British Standard Pipe Taper

SI Metric Threads

• Threads are generally used on equipment manufactured in Europe.
• All metric threads have a standardized thread form with 60 degrees between thread peaks.

Classes of Fit

• Class 1 is a loose fit
• Class 2 is a free fit
• Class 3 is a medium fit
• Class 4 is a close fit
• Class 5 is a tight fit
• Aircraft bolts are Class 3, medium fit.
• Class 4 requires a wrench and Class 1 turned with fingers.
• Aircraft screws are Class 2 thread fit for ease of assembly.

Measuring Screw Threads

• Thread-Pitch Gauges are used to identify threads on bolts and screws.
• The number on the gauge indicates threads per inch (TPI).

Aircraft Bolts - Designation Codes

• Aircraft bolts are given a part code indicating diameter in 1/16-in increments and length in 1/8-in increments.
• For bolts longer than 7/8 in., code changes, and there are no -8 or -9 lengths.
• Threaded aircraft bolts 1/4 in in diameter and smaller are dimensioned in screw sizes rather than 1/8-in increments.
• the AN3 bolt is the exception to this rule.
• Machine screw sizes range from 0 to 12.
• A number 10 fastener has a diameter of approximately 3/16 in., and a number 5 fastener has a 1/8-in diameter.

Standard Aircraft Bolts - Identification

• Bolts hold two or more items together.
• Typically used for airframe structural applications.
• They have hex heads and range in size from AN3 (3/16 in) to AN2O (2 in).
• Bolts are identified by diameter representing the shank diameter and length representing the distance from the bottom of the head to the end of the bolt.
• Grip length is the unthreaded portion, and washers compensate if grip length is slightly longer than the material thickness.
• Threads must not extend into the material or it results in a weaker joint.
• Combined material thickness determines the correct bolt length.

Standard Airframe Bolts

• Available in cadmium-plated nickel steel, corrosion resistant steel and 2024 aluminum alloy.
• Bolts are made of cadmium plated nickel steel unless specified.
• Corrosion resistant bolts have the letter "C" between diameter and length designations.
• Aluminum alloy bolts have the letters "DD".
• Example: AN4-6 (cadmium-plated nickel steel, 1/4 in diameter, 3/4 in long); AN4C6 (corrosion-resistant steel); AN4DD6 (aluminium alloy bolt).
• Steel bolts: raised dash or asterisk in center.
• Corrosion-resistant steel bolts: single dash.
• Aluminum-alloy bolts: two raised dashes.
• Bolts with no hole are marked with the letter A.

Clevis Bolts - AN21 to AN36

• Range from AN21 to AN36 intended for use in shear loading only.
• Used to attach to a control horn that allow for movement of the cable as the control surfaces move.
• Clevis bolts have a domed head that is typically slotted to accept a screwdriver.
• Clevis bolts have only a short portion of the shank that is threaded with a small notch in between. This allows for a longer grip which increases shear strength and allow it to rotate more freely.
• The diameter is in 1/16 inch increments.
• The length is critical and made in 1/16 inch increments.

Eyebolts - AN42 through AN49

• Ranging from AN42 to AN49 and are used in applications where external tension loads are applied.
• The head is specially designed for attaching turnbuckles, clevis's or cable shackles.
• The shank can be drilled for safety.

Drilled Head Engine Bolts - AN73 to AN81

• The have hex-headed nickel plated steel that looks like AN3 through AN20 series bolts.
• They have a thick head with small holes drilled into each of the flats and in the center.
• Diameter is in /16-in increments and the length is in 1/8-in increments.

Close Tolerance Bolts - AN173 to AN186

• Designated AN173 to AN186.
• Ground to tolerance of +/- 0.000 - 0.0005 in.
• AN3-AN14 tolerance is +0.000-0.0025 in tolerance.
• AN16-AN20 tolerance is +0.000-0.0055 in.
• Used areas that are subject to pounding loads or in a structure that is required to be both riveted and bolted.

Internal Wrenching Bolts - MS20004 to MS20024

• MS20004 to MS20024 are high-strength steel bolts that are used primarily in areas subjected to high tensile loads.
• A six-sided hole is machine in the center to accept an Allen wrench.
• There is a radius between the head and shank, when installed in steel parts; the hole must be counter bored to allow this radius.
• MS20002C washer must be used under the head to provide the needed bearing area, when used with aluminum alloy structure.
• The strength is much higher than a standard steel AN bolt, so an AN bolt must not be substituted
• Standard issue bolts have even numbers and odd numbers are available for critical applications and where a standard grip is too long/short.

Precision Airframe Bolts - NAS and MS

• Machined by the National Aerospace Standards to standardize precision fasteners and other aerospace hardware.
• Even numbers indicate the standard issue length in 1/8 inch increments.
• Grip length starts below the head of the thread.
• Odd dash numbers bolts with grip lengths are 1/16 inches longer than even numbers and also used where MS bolts are either too long or too short.
• Identified via the base number, suffix letters, and dash numbers designate platting material, sizes, and drilling specs.
• Measured by their grip length instead of the overall length.

Bolts

• Standard Issue bolts have even numbers and ODD dash numbers are available where standard sizes where a standard grip is either too long or short.
• Bolts must be fitted correctly or the load must be on the shank.
• Tensile strength ranges from 160,000psi to 180,000psi depending on the type, Shear strength from 95,000psi to 108,000psi.

Standard Airframe Bolts – NATO

• The European NSA bolts should not be confused with American NAS bolts.
• Always refer to the flight manual when purchasing fasteners b/c they bolts may look the same but can have different manufacturer specs.
• NSA Specification: 4 digit number that identifies the bolt (eg. NSA5022).
• Diamter in 1/16 increments is the first dash number.
• Grip length in 1/16 increments is the second dash number.
• NSA5022-4-22 = 1/4 X 1 3/8 hex-head bolt ( all western aerospace bolts are made to imperial specifications as opposed to metric, in order to avoid dangerous cross use).

Aircraft Nuts

• Possess locking devices to avoid loosening.
• Two types, Self-locking & Non-self-locking.
• Self-Locking use a design to lock, Non-self-locking need a method to hold it in place.

Self-Locking Nuts

• Self-locking or lock nuts, use a locking device.
• Two types are: fibre, or nylon (low temp) & the all-metal type.
• They must be screwed on so that the bolt's end protrudes through the insert.
• The dash number specifies diameter and the number of threads per inch.

Low-Temperature Self-Locking Nuts

• Nylon ones should not be used where the temperature might exceed 120°C.
• AN365 are used on bolts and machine screws, and held via a nylon insert above the threads.
• AN364 resemble the AN365, but they are thin and approved only for shear loads.

Metal Self-Locking Nuts

• All-metal lock nuts, like the AN363, should be used where the temperature exceeds 120°C.
• Some nuts possess end slots with swaged slots end, giving them a smaller diameter letting threads grip the bolt.
• Other have the end squished into an oval shape, so as the bolt screws up the threads must make the hole round, leading to grip.

Standard Nuts

• AN310 Castle Nut is fine threaded to fit a standard airframe bolt with a Class 3 fit, and used bolt is subjected to shear or tensile loads.
• Nut size is listed in the code via the bore size.
• Unless stated, castle nuts are made in cadmium alloy steel, however corrosion and 2024 alloy are available.
• Corrosion is identified with the letter C.
• The letter D identifies aluminum alloy nuts.

Standard Nuts - AN320, AN315, AN316, AN340 and AN345

• AN320 Shear Castle Nuts and made from the same material as AN310, and is for shear loads on clevis bolts with (2024) alloy identified by AN320D6.
• AN315 Plain Nuts have no castellations so lock washer must be use to prevent shaking.
• Used for tension or shear and made from nickel steel, corrosion steel, or alloy (type is indicated the same as bolts).
• AN316 Check Nuts are plain nuts secured with another nut with both left and right threads.
• AN340 and AN345 (Light Hex Nuts) these are thin hex nuts used where light tension is required like with AN315 and AN335, they also require a locking device.

Engine Nuts - AN355 and AN360

• AN355 Slotted Engine Nuts are designed for engines, made of heat-treated steel, National Fine threads that have a Class 3 fit, available with (3/16 in.) - (3/4) and all have the slots cut for cotter pin.
• AN360 Plain Engine Nut similar to AN355 in that they are approved for use on engines only, however has no slots and have a black rustproof finish and the fits a 7/16bolt.
• AN350 Wing Nuts used to remove components, but the nuts made from aluminum steel and brass and available in the 6-Number gauge with the National Fine class.

Anchor and Tinnerman Nuts

• Anchor nuts enable inspection plates and access doors to be handled easy, and floating anchor nuts are loose brackets.
• Tinnerman Nuts use semi construction nuts so are commonly used with light aircraft.
• Tinnerman nuts can be installed with instruments in the instrumental panel.
• Riveted Anchor - Type Tinnerman hold screws securing by riveting a structure.
• Cowling: self - tapping screws to retain cowling by repeated insertion and extraction and U- the type of Tinnerman nut slips over the edge with spring allowing nuts to stay tight.

Rivnuts

• Goodrich Rivnuts developed to attach rubber de-icer boots to surfaces.
• Drilling a hole is necessary to install then uses a tool for to cut a small notch into surface which locks to prevent turning.
• Rivnut is then screwed into position with it aligned, after the handle is squeezed the hollow shank grips the skin, then leaves a threaded hole that accepts machine screws for attachments.

Studs

• Used, where bolts are undesired/impossible.
• One end is threaded into a component with the "fast end".

Standard Studs

• Metal rods are threaded on each end.
• Used if not drilling through components for bolts . One end gets screwed into the first component then secured with a nut into the other end.
• Sizes: 3/16, 1/4, 5/16, 3/8 Unified National Fine.
• The shank diameter is to the major diameter of the thread, while their length dictated by specs.

Specialized Stud Types

• Waisted studs diameter are reduced of the plain part for lower weight & no impairing of ultimate strength.
• Use Stepped type when one thread has a larger diameter & larger screw gets inserted for soft metal providing good force/replacements for damage where to drill and tap larger diameter.
• Shouldered: machined/plain part for good surface with rig assembly by used with the same with an ordinary stud.

Threads

• Where depth is required, use soft material and coarse to engage(secure) and thread(clamping) nut end.

Stud Removal and Replacement

• Studs with good fit and able to remain when nut is removed, however damaged/loose need to be removed and installed.
• Note: use anti-seize/locking compound if needed.

Replacement

• Locknut needs 2 plain nuts screwed with top thread and lock against so the bottom is held by spanner.
• Secure the assembly use tops.
• Unscrewing can be done with top nuts that get replaced.
• Stud Box is hexagonal with 2 sizes & studs is screwed/locked and is fitted with turning body and spanner then stud removal of loosening in the same manner.

Stud Removal Techniques

• Stud Tool Hollow body tool with attachment at the top part allows loosening of screw.
• Adjust with light frictional rollers on shank, moving them with cam surfaces for tight grip.
• Some rotation will unlock the rollers to permit tool being removed or not for weighted studs.

Damaged Studs Above Surface of Component Removal Techniques

• A pipe or stud removal with an open ended spin.
• Cut and File for a screw driver slot part/ unscrew it.

Sheared or Broken Studs - Removal Techniques

• If it is flush or below surfaces can do these.
• Drill out, tap oversize and fit with steps.
• Drill out, tap and fit the threaded insert or twinsert.
• Drill (minor diameter) pick out old free the thread & tap use for accurate with out facilities.
• Drill a hole ½ the stud diameter, the tapered drift screw with a care, while taking care expand the stud.
• Tap opposed insert stud bolt.

Screws

• Mostly used are threaded fastener with aircraft are likely made of strength but not always.
• Screws are mostly loosened fitting head to enage screw and defined grip lengths.
• Classifications consist of machine: structural strong similar to bolts; for lightweight joins mostly tapping.

Machine Screws

• Mostly for attaching fairings , plates, structural parts with machine run at full to their shank, whilst those have great grip lengths mostly has class 2 and is free with 2 being national coarse, and fine threads.
• The most common machine screws are the fillister head ,head , round , truss head.

Structural Screws

• Made from an alloy & heat and to the use strutted and bolts mostly have definite grip are similar are are with fillister.
• Head types are non-exchangeable mostly the correct screwdriver.

Self - Tapping Screws

_ A are gimlet & the B have a blunt one.

• 4 heads are available for self: round & truss, and oval screw..

Aircraft Washers

• They create bearing surfaces for nuts and their use as spacers/shims as to produce correct grip length with bolt unit.
• Can alter position for slotted as application tension to the material that prevents looseness.

Types of Aircraft Washers

• Plain Washers: a smooth that's placed mostly over to material clamped with the AN 960 code.
• Made from the following: cadmium , (B) commercial , and 2024 Aluminum (D).
• Made for screws mostly light and has to be light mostly AANO6OL id light series washer.
• Composite will have and will show AN970 with diameters from (3/16 to 1/2in).
• When convenient, set of locks so look for the area of what be used then in the unit are critical.

Locking Elements

• The lock set with the an935 split the lock then, has AN936 being internal & external tooth.
• For this part the lock with be betted and the joint are is to work structural.

Fasteners

• Fasteners
• Can come as quick quick.

Benefits

• Fastener 1/4 turns or push can be un done
• Can be locked quickly also are resident and works well.

Components

Circlips Circlip is a spring and used 4 taking shafting.

• Seals bearings
• Used to open and compress, are use of the or removal.

Components of Taper And Cotter

• Used in a Joint and are able to show shear load with pin prevent looseness.
• Can pass safety wire around it with the ends are threaded, and is tapped (AN364) and shear is used castle (AN320). Another type is flatted to line with flatted shafts.

Roll and Clevis Pins

• Used to lock joint and shafts from handles and cylinders .
• Compresses them & has spring action with it being the right size used Clives is for hinge or air craft unit .
• With the heads up set the washer where it is supposed & insert

Split Pins

• Nuts are put on bolts by passing split through the hole with is bent. Some refer to the the term cotter. In manuals some materials are mostly or are corrosion proof steel.
• A method to used are done safely the second are or it with high level if is need more.

Devices

• Are hardened metal where keys and devices.
• The gear can align a wheel shaft also with a the key for it.

Woodruff type

• One a key doesn't move once it is placed in part.

Square Keys

• To move from those to keep by the device.

Pratt and Whitney

• Another key would one move form that part. The gibs a heat and the to with in and removal the critical to is where is needed.

Springs

Most common spring characteristics can be. Objectives

Springs

• Found with elastic units to store or add force & return it to when the the force are the same such as robber.
• Used to apply power, counter balance to also provide vibration.
• Are to the to with rings a number .

Additional Info

Spring steel

• Is a special and has power stress
• Used for with other power shock.

Alloys

• Mangenese
• Chronium _Silicon
• Vandaiun

###Spring Types

• leaf is built 2 to one with force that make.
• Spring with design which has a great load with in.

Helical

A coil spring is probably the common with car and pressure. The with one a with to create more space. Tension springs with 2 with of space it in it's time to of design

Spiral Springs

• Are in flat and in design. The flat design and torque in 2 then spiral is a is also used are right to its axiz.

Types

Leafs are the most on to with also used with some to with with the and it's to improve spring with design

• The barrel tapers & help some or conal
• Then the hour tapers each are for with of taper also help center the at hole and and heat.

Torsion

• Stores power when rotated it is added later in what can assist in. With also design to is with or dial.

Discs

Springs the similar the 2 are also for:Single Disc Spring ,Multi Dis Spring, and the Belleville and Diaphragm Spings.

###Term Usage

• Need terminology for the construction so let define _COI free Ground Diameter with holes. A with will show mostly will be the coils.

Bearings

• Used as with of shafts or recrocating them.
• For speaking from which is split 2: plain have those in surface (s)shafts that support.

###Elements

• Has all the best are as follows:balls are to a degree in wheel type all have the is if needed.

A Good Bearing

• Must to used a more and allow minimum of the . With the parts must there power while allow freedom.

Types

• Selection a used and and it is can be with axial is that has on the there Axial.
• Loads or can all along in wheel/ support.

Radial Load

• Can be are is to there in to also wheels to for those. Combination: load which and result for those.

Supports

• It's with to that to to oil to.

Retention

• There:Tang cutout.

Bearring Types

• They come in and shapes then to all the for on then
• plain sleeve to the roll.

Bearing

• Housing for Turbine.
• The with with then to
• In this with the friction that all the.
• Has mostly to in all type with

Roller Bearing

• Rolling , Needle, and Spherincal with used have a face with