Aircraft bolts, nuts, rivets and safety wire for the A&P General

Hardware questions reward memorized codes: what an AN part number means, what the head markings say, when a self-locking nut can be reused, and the safety wiring rules the FAA handbook spells out.

Questions and answers, explained

All 12 questions above, with the correct answer and why it is correct. Everything here is on aircraft bolts, nuts, rivets and safety wire for the a&p general.

1. An AN bolt with two raised dashes on its head is made of

   • Acorrosion-resistant steel
   • Bcadmium-plated carbon steel
   • Caluminum alloyCorrect
   • Dtitanium alloy

   Why: AN head markings: a cross or asterisk for standard alloy steel, a single raised dash for corrosion-resistant steel, and two raised dashes for aluminum alloy. A triangle marks a close-tolerance bolt.

   Reference AM.I.E.K11 · FAA-H-8083-30B, Ch. 7 (Identification and Coding of Bolts)

2. A raised or recessed triangle on the head of a bolt identifies it as

   • Aa close-tolerance boltCorrect
   • Ban aluminum-alloy bolt
   • Ca bolt that failed magnetic inspection
   • Da bolt drilled for safety wire

   Why: The handbook: close-tolerance NAS bolts are marked with a raised or recessed triangle. Close-tolerance bolts are machined more accurately and are used where a tight drive fit is required.

   Reference AM.I.E.K11 · FAA-H-8083-30B, Ch. 7 (Close Tolerance Bolts)

3. In the part number AN3DD5A, what does the 3 indicate?

   • AA length of 3/8 inch
   • BA diameter of 3/16 inchCorrect
   • CThread class 3, fine fit
   • DA grip of 3 inches

   Why: The handbook decodes AN3DD5A this way: 3 is the diameter in sixteenths of an inch (3/16), DD means 2024 aluminum alloy, 5 is the length in eighths of an inch (5/8), and A means the shank is undrilled.

   Reference AM.I.E.K11 · FAA-H-8083-30B, Ch. 7 (Identification and Coding of Bolts)

4. Elastic stop nuts with a fiber insert should not be installed where the temperature exceeds

   • A450 °F
   • B160 °F
   • C1,000 °F
   • D250 °FCorrect

   Why: The handbook: do not install elastic stop nuts where the temperature is higher than 250 °F, because the self-locking action is reduced beyond that point. All-metal self-locking nuts are used in hotter locations.

   Reference AM.I.E.K9 · FAA-H-8083-30B, Ch. 7 (Elastic Stop Nut)

5. When may a used elastic stop nut be reinstalled?

   • ANever; fiber-insert nuts are single use
   • BOnly if the fiber still grips and it cannot be turned by handCorrect
   • COnly after the fiber insert has been tapped
   • DAny time, as long as it is lubricated first

   Why: Elastic stop nuts can be reused many times, but the handbook says to make sure the fiber has not lost its locking friction or become brittle, and to replace any nut that can be turned with the fingers. Never tap the fiber insert; the bolt threads must impress themselves into it.

   Reference AM.I.E.K4 · FAA-H-8083-30B, Ch. 7 (Elastic Stop Nut)

6. Which is a general safety wiring rule from the FAA handbook?

   • AWire may be reused if it is not kinked
   • BThe pigtail should be left straight so it is easy to see
   • CLoosen a torqued nut slightly to align the holes
   • DUse new wire every time, with a 1/4 to 1/2 inch pigtail bent backCorrect

   Why: Safety wire must be new on each application. The pigtail at the end is 1/4 to 1/2 inch (three to six twists) and must be bent back or under so it cannot snag. Never loosen or over-torque a torqued nut to align holes.

   Reference AM.I.E.K5 · FAA-H-8083-30B, Ch. 7 (General Safety Wiring Rules)

7. When safety wiring a group of widely spaced bolts by the double-twist method, what is the maximum number in one series?

   • AThreeCorrect
   • BTwo
   • CSix
   • DAs many as a 24-inch wire reaches

   Why: The handbook: for widely spaced bolts by the double-twist method, a group of three is the maximum in a series. The 24-inch length limit applies to closely spaced bolts. Either way the wire is arranged so loosening pulls it in the tightening direction.

   Reference AM.I.E.K5 · FAA-H-8083-30B, Ch. 7 (Safety Wiring)

8. A nut must be torqued to 300 inch-pounds using a torque wrench 10 inches long with a 2-inch extension in line with it. What should the wrench read?

   • A360 inch-pounds
   • B300 inch-pounds
   • C250 inch-poundsCorrect
   • D240 inch-pounds

   Why: Use the extension formula: wrench reading = desired torque × L ÷ (L + E) = 300 × 10 ÷ 12 = 250 in-lb. The extension adds leverage, so the dial must read less than the torque actually applied.

   Reference AM.I.E.K8 · FAA-H-8083-30B, Ch. 7 (Torque; Figure 7-33)

9. Why are bolts and nuts tightened to a specified torque value?

   • ATo keep the threads from being lubricated
   • BSo the nut can be removed easily later
   • CTo make the bolt carry the load in bending
   • DTo develop the designed preload without overstressingCorrect

   Why: Torque is how the technician produces the correct preload, the clamping tension in the bolt. Too little lets the joint shift and fatigue the bolt; too much can stretch or strip it. That is why torque values and correct lubrication matter.

   Reference AM.I.E.K10 · FAA-H-8083-30B, Ch. 7 (Torque)

10. Which rivet, known as the field rivet, is used more than any other for riveting aluminum alloy structures?

    • A1100
    • B2017-T
    • C2117-TCorrect
    • D5056

    Why: The handbook calls the 2117-T rivet the field rivet, the most widely used rivet on aluminum alloy structures. It needs no heat treatment before driving. 2017-T and 2024-T are icebox rivets, 1100 is for soft aluminum, and 5056 is for magnesium.

    Reference AM.I.E.K4 · FAA-H-8083-30B, Ch. 7 (Rivets)

11. Why are 2024-T icebox rivets kept in a refrigerator after heat treatment?

    • ATo delay age hardening so they stay soft enough to driveCorrect
    • BTo prevent corrosion of their protective coating
    • CTo make them harder before they are driven
    • DTo shrink them so they fit tighter holes

    Why: Heat-treatable 2017-T and 2024-T rivets begin to age harden within minutes at room temperature. Cold storage keeps them soft enough to drive for up to two weeks; after that, or after an hour or more at room temperature, they need reheat treatment.

    Reference AM.I.E.K2 · FAA-H-8083-30B, Ch. 7 (Rivets; Icebox Rivets)

12. The rivets in a lap joint are mainly loaded in

    • Atorsion
    • Bcompression
    • Cbending
    • DshearCorrect

    Why: Shear is the stress that tends to slide one layer of material past another. In a lap joint the two sheets pull in opposite directions and try to slice each rivet across its shank, so rivets are primarily shear fasteners.

    Reference AM.I.E.K3 · FAA-H-8083-30B, Ch. 7 (Stresses; Shear)

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