Standard Aircraft Bolts Quiz

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Questions and Answers

What does the grip length of a bolt refer to?

The distance from the bottom of the head to the end of the bolt

The total length of the bolt including the head

The unthreaded portion of the bolt (correct)

The overall diameter of the bolt

How is the diameter of a standard aircraft bolt indicated in its designation?

By a letter before the number

By the length specified in increments

By the number immediately following the prefix (correct)

By the dash number in the code

What will occur if the grip length of a bolt is substantially less than the combined thickness of the materials being joined?

The bolt's threads will disturb the joint

The bolt can create a weak joint (correct)

The bolt will not fit properly

The joint will become stronger

Which material is a bolt made from if it carries the designation AN4C6?

Corrosion-resistant steel Signup and view all the answers

What does the dash number in a standard aircraft bolt code indicate?

The length in 1/8-inch increments Signup and view all the answers

If a bolt is identified as AN3-6A, what does '3' represent?

A diameter of 3/16 inches Signup and view all the answers

What type of bolt is identified by the letters 'DD' in its code?

2024 aluminium alloy Signup and view all the answers

What happens if a nut is unable to provide proper pressure when tightened?

The joint might fail Signup and view all the answers

What does the code AN4C6 signify about a bolt?

It is made of corrosion-resistant steel Signup and view all the answers

What marking indicates that a bolt is made of aluminium alloy?

Two raised dashes Signup and view all the answers

What indicates that an AN bolt does not have a drilled shank?

The presence of the letter A Signup and view all the answers

What is a distinct feature of a clevis bolt?

A slotted head typically Signup and view all the answers

For which purpose are eyebolts designated AN42 to AN49 used?

External tension loads Signup and view all the answers

What is the primary difference between drilled-head engine bolts and standard AN bolts?

Drilled-head engine bolts have a thicker head Signup and view all the answers

How are close tolerance bolts designated?

AN173 to AN186 Signup and view all the answers

What must be used under the head of an internal wrenching bolt installed in aluminum alloy?

A MS20002C washer Signup and view all the answers

What type of marking is used on close tolerance bolts?

Triangle mark Signup and view all the answers

What does the letter H indicate in the part number of a bolt?

That the bolt has a drilled head Signup and view all the answers

What does the term 'grip length' refer to?

The distance from the bolt's head to the first thread Signup and view all the answers

What is a common application of internal wrenching bolts?

In high tensile load areas Signup and view all the answers

What do odd dash numbers signify in National Aerospace Standards?

Special application bolts Signup and view all the answers

What is the tolerance of close tolerance bolts compared to standard AN bolts?

+0.000–0.0005 in. Signup and view all the answers

What must be ensured when fitting aircraft bolts?

The load must be on the shank and not on the thread Signup and view all the answers

Which bolt type is identified by a four-digit NSA specification number?

NSA Bolts Signup and view all the answers

What feature is essential in all aircraft nuts to prevent loosening?

A locking device Signup and view all the answers

What is a critical temperature limit for low-temperature self-locking nuts?

120 °C Signup and view all the answers

Which self-locking nut type is designed for use in high-temperature applications?

All-metal self-locking nut Signup and view all the answers

What function does the plain portion of a waisted stud serve?

It serves to reduce the weight while maintaining strength. Signup and view all the answers

When would a stepped stud be most effectively used?

As a replacement for damaged studs drilled to a larger diameter. Signup and view all the answers

What does the first dash number in an NSA bolt specification denote?

Diameter in 1/16 in. Signup and view all the answers

What occurs if more than three threads are exposed on a self-locking nut?

It risks under-torquing the assembly Signup and view all the answers

What is the primary purpose of an integral shoulder on a shouldered stud?

To provide a more rigid assembly. Signup and view all the answers

Which type of nut is specifically not to be used in tension?

AN364 thin nut Signup and view all the answers

What is the main advantage of using locknuts during stud replacement?

They ensure a tight fit without movement. Signup and view all the answers

Which tool is specifically designed to accommodate different stud sizes during replacement?

Stud Box Signup and view all the answers

What is the primary material distinction for corrosion-resistant nuts?

Identified by the letter 'C' before the dash number Signup and view all the answers

What type of lock nut uses a nylon insert to secure itself?

AN365 nut Signup and view all the answers

Why should a stud be a good fit when installed?

To remain in place when the nut is removed. Signup and view all the answers

Which specification indicates a self-locking nut that fits a 5/16-in. fine-thread bolt with 24 threads per inch?

-524 Signup and view all the answers

What does the method of stud removal using a universal stud extractor not guarantee?

Preservation of the stud's integrity. Signup and view all the answers

What should be applied to a stud prior to replacement if specified?

Anti-seize or locking compound Signup and view all the answers

What defines the AN310 Castle nut in terms of its application?

Designed for both shear and tensile loads Signup and view all the answers

What characteristic does an AN320 Shear Castle nut have compared to an AN310 nut?

It is much thinner and used only for shear loads Signup and view all the answers

When removing a stud that is flush or below the surface of a component, what is the recommended first step?

Drill out the stud to extract it. Signup and view all the answers

Which type of stud may require the use of a coarse series thread at the fast end for better engagement?

Shouldered Stud Signup and view all the answers

What locking mechanism must be used in conjunction with an AN315 Plain nut?

Lock washer Signup and view all the answers

Which feature of a stepped stud enhances its holding power?

Larger major diameter of the threaded end. Signup and view all the answers

What is a common consequence of using stud removal wrenches on studs?

They can break the stud during removal. Signup and view all the answers

Why are waisted studs designed with a reduced diameter?

To maintain strength while reducing weight. Signup and view all the answers

Which method would NOT be appropriate for stud removal when the stud is sheared or broken below the surface?

Using locknuts to grip the stud. Signup and view all the answers

What identifies nickel steel in the designation code?

Absence of an additional letter Signup and view all the answers

Which type of nut is suitable for left-hand threads?

AN315C-4L Signup and view all the answers

Which nut requires a locking device to secure it?

Wing nut Signup and view all the answers

What is a characteristic of the AN360 engine nut?

It has a black rustproof finish. Signup and view all the answers

What is the purpose of a spring-type lock washer used with AN315 nuts?

To apply spring force preventing the nut from loosening. Signup and view all the answers

What does the designation 'AN350-616' indicate?

It is a wing nut size for a 3/8-in bolt. Signup and view all the answers

What distinguishes Rivnuts from regular nuts?

They have a threaded hole for machine screws. Signup and view all the answers

Which type of nut is designed specifically for use in aircraft engines?

AN360 Signup and view all the answers

What type of threads do Wing nuts have?

National Fine threads Signup and view all the answers

Why are Tinnerman nuts made of brass?

To reduce electromagnetic interference. Signup and view all the answers

What feature do AN355 slotted engine nuts have?

They have slots cut for a split pin. Signup and view all the answers

How is a floating anchor nut installed?

It fits loosely into a bracket riveted to the skin. Signup and view all the answers

Which material is NOT mentioned as being used for AN315 nuts?

Plastic Signup and view all the answers

What is a common application for Tinnerman nuts in light aircraft?

Mounting instruments to the instrument panel. Signup and view all the answers

What does the absence of split pin slots in the AN360 suggest?

It is not made for secure installations. Signup and view all the answers

Study Notes

Aircraft Bolts Overview

Bolts are crucial for holding structural components together in aircraft.
Common size range for aircraft bolts is AN3 (3/16 in.) to AN20 (2 in.).
Identification is based on diameter (shank diameter) and length (from bottom of head to end).

Grip Length and Washers

Grip length is the unthreaded portion of the bolt.
Longer grip lengths may require washers to ensure proper pressure when tightened.
Insufficient grip length can lead to weakened joints due to thread extension into materials.

Bolt Designation System

Diameter indicated by number following 'AN' (e.g., AN4 = 1/4 in.).
Dash numbers specify length in 1/8 in. increments.
A lacks a split pin hole; no letter indicates a drilled shank.

Material Types for Aircraft Bolts

Common materials include cadmium-plated nickel steel, corrosion-resistant steel, and 2024 aluminium alloy.
Corrosion-resistant bolts incorporate the letter C in the designation (e.g., AN4C6).
Aluminium alloy bolts use DD in the designation (e.g., AN4DD6).

Bolt Head Markings

Materials marked to identify bolt type; nickel steel bolts often have a raised dash or asterisk.
Corrosion-resistant steel has a single dash; aluminium alloy bolts have two raised dashes.

Clevis Bolts (AN21 to AN36)

These bolts are only loaded in shear and feature a domed head, suitable for control cables.
Short shank with a notch enhances shear strength while allowing free rotation.

Eyebolts (AN42 to AN49)

Designed for applications with external tension loads, they can attach turnbuckles or cable shackles.

Drilled-Head Engine Bolts (AN73 to AN81)

These bolts have a larger head with drilled holes and are used in engine applications.
They maintain similar diameter and length measurements found in other bolt series.

Close Tolerance Bolts (AN173 to AN186)

Manufactured to strict tolerances (+0.000–0.0005 in.) for demanding structural applications.
Identifiable by a triangle mark on their heads.

Internal Wrenching Bolts (MS20004 to MS20024)

High-strength steel bolts with a six-sided hole for Allen wrenches.
Require special washers when used with aluminium structures.

Precision Airframe Bolts

Following NAS standards, precision bolts have grip lengths measured from under the head.
Odd dash numbers provide alternative sizing for critical grip lengths.

NATO Standardisation Agency Bolts

European NSA bolts differ from American NAS bolts; always refer to parts manuals for accuracy.

Types of Aircraft Nuts

Aircraft nuts must have locking mechanisms to avoid loosening.
Basic types include self-locking and non-self-locking.

Self-Locking Nuts

Two types exist: nylon (low temp, maximum 120 °C) and all-metal.
Proper installation prevents ‘bottoming out’ which can create stress points.

Specific Types of Nuts

AN310 Castle Nut: Fits standard airframe bolts; used for shear or tensile loads.
AN320 Shear Castle Nut: Thinner than standard nuts; only for shear loads.
AN315 Plain Nut: Lacking castellations; requires a lock washer for stability.

Special Application Nuts

AN340 and AN345: Light hex nuts for non-structural applications requiring light tension.
AN355: Slotted engine nut for use only in engine applications, available in many sizes.
AN360: Plain engine nut with no slotted design, also engine-specific.

Unique Nut Types

Anchor Nuts: Permanently mounted nuts for easy access to inspection plates; floating types assist alignment.
Tinnerman Nuts: Economically stamped nuts, often used in light aircraft for instrument installation.
Rivnuts: Developed for mounting de-icer boots; lock into skin to prevent rotation during installation.### Rivnuts
Rivnuts create a threaded hole in surfaces, allowing machine screws for de-icer boot attachment.
Widely used in aviation and automotive industries.

Studs

Studs are threaded metal rods with threads on both ends.
Ideal for situations where drilling through both components for bolts is impractical.
One end is screwed into a tapped hole (fast end), while the second component is secured by a nut on the other end.

Types of Studs

Standard Studs: Available in sizes: 3/16, 1/4, 5/16, and 3/8 Unified National Fine. Lengths vary based on part numbers and specifications.
Waisted Studs: Lighter design due to reduced diameter on the plain portion, maintaining strength.
Stepped Studs: Feature different diameters on each end, with larger threads providing more grip in softer materials.
Shouldered Studs: Include a shoulder for better assembly rigidity and depth of engagement; coarse threads on one end and fine threads at the nut end.

Stud Replacement

Proper fitment is crucial for studs; damaged or loose studs must be replaced.
Anti-seize or locking compound should be applied before replacement as directed.

Methods of Stud Replacement

Locknut Method: Two plain nuts lock against each other; lower nut is held while the upper is tightened to screw the stud in place.
Stud Box: A hexagonal device that holds two stud sizes and is turned with a spanner; prevents stud damage during insertion/removal.
Stud Tool: Hollow body with rollers that grip the stud; allows for controlled insertion/extraction without damaging threads.

Stud Removal Techniques

Loose or intact studs can be removed using locknuts, stud tools, or universal stud extractors.
Universal Stud Extractors: Use a knurled wheel that grips the stud; initial motion aligns and grips to turn the stud for removal.

Dealing with Damaged Studs

Protruding Studs: Can be removed using a pipe wrench, by filing flats for an open-ended spanner, or creating a screwdriver slot.
Flush or Broken Studs: Options include:
- Drilling and tapping for a new stud or threaded insert.
- Using precise drilling techniques to remachine threads.
- Inserting a tapered drift to unscrew when partially embedded.

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Description

Test your knowledge on standard aircraft bolts used in airframe structural applications. This quiz covers the identification, sizes, and specifications of different types of bolts, including their grip lengths. Perfect for aviation enthusiasts and students!