Aircraft Nut Standards Quiz

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Questions and Answers

What is the minimum extension of a flat end bolt through a nut after tightening?

1/2 inch

1/32 inch (correct)

1 thread

1/16 inch

Which of these conditions is acceptable for using self-locking nuts?

With damaged threads on bolts

When tapping the nylon locking insert

In areas with temperatures below 250 °F (correct)

Only when specified by the bolt manufacturer

How many threads should normally be visible above a tightened nut?

3 to 5 threads

1 to 3 threads (correct)

5 to 7 threads

No threads should be visible

What is a potential issue when using bolts with rough ends?

Reduced self-locking effectiveness Signup and view all the answers

What feature characterizes the removable type of self-locking nut bases?

They allow for floating nuts Signup and view all the answers

What is the effect of temperature on the performance of self-locking nuts?

Effectiveness is reduced beyond 250 °F Signup and view all the answers

What maintenance action should not be performed on the nylon locking insert of self-locking nuts?

Tapping the nylon locking insert Signup and view all the answers

In what scenario can bolts with cotter pin holes be used with self-locking nuts?

If they are free from burrs around the holes Signup and view all the answers

What does the letter 'B' signify when following a part number for aircraft nuts?

Brass Signup and view all the answers

Which material is indicated by the letter 'D' in aircraft nut identification?

2017-T Aluminum Alloy Signup and view all the answers

What does the dash (-) indicate when used in place of a letter in the part number?

Cadmium-plated Carbon Steel Signup and view all the answers

How does the dash number in the part number relate to the size of the shank and threads?

It shows the size of the bolt that the nut will fit. Signup and view all the answers

What do the last two digits in the code numbers for self-locking nuts represent?

Threads per inch Signup and view all the answers

An aircraft nut identified as 'AN315-3' would fit which size bolt?

AN3 (10-32) Signup and view all the answers

What does a two-digit number following the material code signify?

The size of the nut in 16ths of an inch Signup and view all the answers

Which material is represented by 'DD' in the part number of aircraft nuts?

2024-T Aluminum Alloy Signup and view all the answers

What is the primary purpose of the AN970 steel washer?

To prevent crushing the surface on wooden structures Signup and view all the answers

Which statement about lockwashers is true?

AN935 lockwashers use spring action to prevent loosening Signup and view all the answers

Under which condition should lockwashers be avoided?

With fasteners that require frequent removal Signup and view all the answers

What feature distinguishes shakeproof lockwashers?

They have tabs or lips that lock the nut in place Signup and view all the answers

Which type of washer is indicated by the letter 'L' in its designation?

Thin or light washer Signup and view all the answers

Where should washers not be used due to corrosive conditions?

With fasteners exposed to the weather Signup and view all the answers

What is a function of the internal tab on a shakeproof lockwasher?

To fit a keyed bolt and secure the lockwasher Signup and view all the answers

Why should lockwashers not be used with fasteners on primary aircraft structures?

To prevent failure that could damage the aircraft Signup and view all the answers

What does the code number AN310D5R indicate about the nut?

It is a castle nut made of 2017-T aluminum alloy. Signup and view all the answers

Which of the following is true about the AN320-10 nut?

It has a diameter of 5⁄8 inches and 18 threads per inch. Signup and view all the answers

What material is specified for the AN350B1032 wing nut?

Brass Signup and view all the answers

Which type of washer should be used under a lockwasher to prevent surface damage?

Plain Washer Signup and view all the answers

When are aluminum and aluminum alloy washers appropriate to use?

Under bolt heads or nuts on aluminum or magnesium structures. Signup and view all the answers

What is a key function of plain washers in bolt and nut assemblies?

Providing a smooth bearing surface for bolt rotation. Signup and view all the answers

What is a disadvantage of using aluminum alloy washers directly under a nut against a steel structure?

They can lead to corrosion from dissimilar metals. Signup and view all the answers

Which characteristic distinguishes an AN310 aircraft castle nut from other types?

It is made from 2017-T aluminum alloy. Signup and view all the answers

Why are aluminum alloy bolts and nuts avoided in maintenance and inspection applications?

They are prone to fatigue over repeated removals. Signup and view all the answers

What is a primary reason for avoiding aluminum alloy nuts with cadmium-plated steel bolts on seaplanes?

Dissimilar metal corrosion is more likely. Signup and view all the answers

How do close tolerance bolts differ from general-purpose bolts?

Close tolerance bolts are machined to tighter specifications. Signup and view all the answers

What unique feature do drilled head bolts possess?

They are interchangeable with standard hex bolts. Signup and view all the answers

In which scenario would close tolerance bolts typically be used?

Where significant vibrations and load reversals are expected. Signup and view all the answers

Which of the following statements about internal wrenching bolts is true?

They require countersinking in steel parts. Signup and view all the answers

What is the key characteristic of the internal wrenching bolt's head?

It has a recessed design for using an internal wrench. Signup and view all the answers

What material composition does Dural represent?

A combination of Aluminum, Copper, and Magnesium. Signup and view all the answers

What type of bolts should be replaced with internal wrenching bolts?

Standard AN hex head bolts Signup and view all the answers

Which of the following is NOT a permissible application for clearance in bolt holes?

Critical structural components Signup and view all the answers

Why do bolts not become swaged to fill oversized holes like rivets do?

They must maintain their shape for proper function. Signup and view all the answers

What must be considered when dealing with oversized or elongated holes in noncritical members?

Drilling or reaming to the next larger size is usually permissible. Signup and view all the answers

What is the maximum clearance specified for light drive fits of bolts?

0.0015 inches Signup and view all the answers

Which type of bolts are used in light drive fit applications?

Standard AN hexagon bolts Signup and view all the answers

What happens when a bolt is installed in an oversized hole?

The bolt carries no shear load until parts have yielded. Signup and view all the answers

Which factor must be considered when sizing bolt holes for primary connecting elements?

Edge distance and load factor Signup and view all the answers

Study Notes

Aircraft Nuts

After tightening a nut, ensure the rounded or chamfered end of the bolt, stud, or screw extends at least the full length of the chamfer through the nut.
A standard practice is to show 1 to 3 threads above the nut.
Flat end bolts, studs, or screws need to extend at least 1/32 inch through the nut.
Bolts with a 5/16-inch or greater diameter with cotter pin holes can be used for self-locking nuts but only if free from any burrs around the holes.
Bolts with damaged threads and rough ends are not acceptable for use.

Aircraft Nuts - Nylon Locking Insert

Do not tap the nylon locking insert.
The self-locking action of an elastic stop nut involves the bolt threads impressing themselves into the untapped nylon.
Avoid installing elastic stop nuts in locations where temperatures exceed 250°F (e.g., exhaust components). Temperatures exceeding this point reduce self-locking effectiveness.
Self-locking nuts are acceptable for use on aircraft engines and accessories when the engine manufacturer specifies their use.

Aircraft Nuts - Self-Locking Nut Bases

Self-locking nut bases use a variety of forms and materials for riveting and welding to aircraft structures or parts (Refer to figure 7-29).
Certain applications require installing self-locking nuts in channels. This arrangement allows for attaching multiple nuts with minimal rivets.

Aircraft Nuts - Identification and Coding

Part numbers identify the specific types of nuts (Refer to figure 7-25).
Plain, AN315 (Fine) and AN335 (Coarse); Castle AN310; Plain check, AN316; Light hex, AN340 (Fine) and AN345 (Coarse); Castellated shear, AN320.
Patented self-locking nuts use part numbers from MS20363 through MS20367. This group includes Boots, Flexloc, fiber locknut, elastic stop nut, and self-locking nut.
Wing nuts use part number AN350.
Additional code number information for various nuts is available in other figures.
Letters and numbers that follow a part number signify material, size, thread type (e.g., right-hand or left-hand), and threads per inch.
B signifies Brass; D signifies 2017-T aluminum alloy; DD signifies 2024-T aluminum alloy; C signifies stainless steel; and a dash (--) signifies a cadmium-plated carbon steel.

Aircraft Washers

Aircraft washers used in the airframe, are available as plain, lock, or special-type washers.
Plain washers AN960 and AN970 are used beneath hex nuts (Refer to Figure 7-30). These washers create a smooth bearing surface for the rotation of a bolt and are used as shims for adjusting bolt and nut assembly grip length..
Plain washers are used to adjust the position of castellated nuts relative to drilled holes for cotter pins.
Plain washers are used under lock washers to protect the surface material from damage.
If used with aluminum or aluminum-alloy components and magnesium/aluminum alloy structures, utilize aluminum alloy washers to mitigate corrosion. However, cadmium plated steel washers are often more effective in preventing damage of nuts when bearing directly on a structure.
Steel washers AN970 have a greater surface area. These are used on wooden structures
Letter "L" in an AN960-416L designation indicates a thin or light-weight washer.
Lockwashers, AN935 and AN936, are used with machine screws and bolts (Refer to figure 7-30). These washers support self-locking or castellated-type nuts where needed and provide enough friction to prevent loosening due to vibration.
Lockwashers are not used with fasteners in primary or secondary structures, fasteners on any part where failure could harm personnel, joining a structure open to the airflow, or bolts subject to frequent removal.
Avoid lockwashers if they are exposed to corrosion or beneath soft materials since they can damage surfaces.
Shakeproof lockwashers, round in shape with tabs or lips bent upwards on the sides are used to secure hex nuts and bolts (Refer to figure 7-30). There are several ways to secure the lockwasher, and the washers can endure higher temperatures and high vibration. The tabs should only be bent once as subsequent bending can break them.
Ball socket and seat washers AC950 and AC955 used for bolts installed at angles to a surface to provide precise alignment.
NAS143 and MS20002 washers are used for internal wrenching bolts from the NAS144 through NAS158 series, and can be plain or countersunk (depressed).
The countersunk washers are designated as NAS143C and MS20002C; designed to allow for clearance for the radius of the bolt head; plain washers are used beneath the nut.
The NAS143C and MS20002C washers are used for internal wrenching bolts part 7-37

General Purpose Bolts

The hex-head aircraft bolt (AN-3 through AN-20) is suitable for different applications with tension or shear. A 0.006-inch clearance is common for a 5/8 inch hole, with other sizes proportionately adjusted.
Alloy steel bolts under AN No. 10-32 and aluminum alloy bolts under 1/4 inch in diameter should not be used on primary structures.
Aluminium alloy nuts may be used with cadmium plated steel bolts. These components can be used for aircraft that aren't seaplanes to prevent corrosion.
AN-73 drilled head bolts are comparable to standard hex bolts but have deeper drilled heads for safety-wire attachments.. AN-3 bolts are interchangeable with AN73 bolts
Close tolerance bolts are machined precisely. They come with hex heads (AN-173 to AN-186) or countersunk heads (NAS-80 to NAS-86). These are used for applications requiring a precise fit, achieved using a 12- to 14-ounce hammer.

Internal Wrenching Bolts

Internal wrenching bolts (MS-20004 to MS-20024 or NAS-495) are fabricated from high-strength steel and are suitable for both tension and shear applications.
For steel components, countersink the bolt hole to accommodate the bolt's head's large corner radius. This feature contributes to the bolt's strength.
In Dural (a high-strength aluminum alloy) materials, a specialized heat-treated washer ensures adequate bearing surface for the bolt head.
The internal wrenching bolt's head is recessed for easy internal wrench insertion and removal.
Bolts are used with special high-strength nuts.
Replace internal wrenching bolts with others of the same type.
Standard AN hex head bolts and washers are not suitable replacements due to their weaker strength.

Installation of Nuts, Washers, and Bolts

Use slight clearances for bolt holes whenever bolts are subject to tension and do not involve reversal of load. This is common in pulley brackets, conduit boxes, lining trims, and miscellaneous brackets.
Make bolt holes perpendicular to the surface to maximize bearing surface for the bolt's head and nut; avoid oversized or elongated holes.
Bolts will transfer shear load only after the surrounding components have yielded to create bearing surface contact. Unlike rivets, bolts don't fill the hole by being swaged (permanently deformed).
For overly sized or elongated holes on critical components, consult the aircraft/engine manufacturer for appropriate bolt selection.
Factors such as edge distance, clearance, and load factor should be considered when selecting and installing bolts.
Oversized or elongated holes in non-critical members can often be reamed to accommodate the next larger bolt size.
The use of slightly larger sized drilled holes with a letter designation is acceptable, except in cases using AN hexagon bolts or NAS style close tolerance bolts.
Light drive fits, requiring a light blow of a 12- to 14-ounce hammer to create movement, are acceptable. Heavy blows to move a bolt suggest too tight a fit.
The term "light drive fit" defines movement with body weight pressure when holding the hammer-handle against the head of the bolt.
Examine bolt markings to ensure proper material.
Reuse similar type bolts in replacement.
Follow Maintenance Instructions Manual and Illustrated Parts Breakdown.
Install washers under both the bolt head and nut unless the instructions specify their omission.
Use washers to prevent mechanical damage to the component and to help prevent corrosion.
Aluminum alloy washers are typically used beneath steel bolts when attaching aluminum and magnesium members because corrosion tends to preferentially attack the washer rather than the members.
Steel washers are used when connecting steel members with steel bolts.
Position the bolt head up or forward whenever possible to prevent slipping in case the nut is unintentionally lost or detached.
Ensure the bolt's grip length matches the material thickness being fastened.
Slightly longer grip length bolts may be used by adding washers under the nut or bolt head..
Use shims under plate nuts to ensure proper mounting.
Safety bolts and nuts require safety wire after installation to prevent loosening from flight vibrations.
All bolts and nuts (excluding self-locking types) should be safety-wired.

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Description

Test your knowledge on the specifications and characteristics of aircraft nuts, including self-locking types and maintenance practices. This quiz covers essential details such as proper use, identification codes, and performance factors to ensure safe and effective fastening in aviation.