Identifying Aircraft Hardware for the A&P Practical

October 25, 2026 · Primary sources checked October 20, 2026

For Airframe and Powerplant (A&P) practical hardware identification, rehearse the O&P (oral and practical) task with the part, its marking and the applicable reference together on the bench.

What does this O&P task evaluate?

The Federal Aviation Administration (FAA) Airman Certification Standards (ACS) identify the marking-based identification skill used in this guide.

The practical project format is one skill element accompanied by two practical questions. The applicant may use available, applicable reference material for the demonstration and the questions.

Order 8900.1, Vol. 5, Ch. 5, Sec. 11, CHG 929, printed 16, PDF 16, 5-5-11-7C3)c)

A pass/fail standard applies to each individual practical project. A passing project depends on first-attempt success in the skill demonstration and successful answers to the two related questions.

Order 8900.1, Vol. 5, Ch. 5, Sec. 11, CHG 929, printed 16, PDF 16, 5-5-11-7C3)f)

You must complete the project to the required performance standard to pass, and the examiner can find that standard in the downloaded test. The FAA Mechanic Test Generator (MTG) FAQ says each practical project is standalone; projects can no longer be combined during testing.

Order 8900.1, Vol. 5, Ch. 5, Sec. 11, CHG 929, printed 16, PDF 16, 5-5-11-7C3)g) · FAA Mechanic Test Generator FAQs, updated May 22, 2023, unnumbered page, PDF 4

The FAA’s sample oral and practical test is marked as a sample test for practice purposes only.

FAA sample oral and practical test, unnumbered page, PDF 6

FAA-S-ACS-1, printed 7, PDF 12

The same ACS subject also lists used hardware or suspected unapproved parts (SUPS) as a risk-management element (AM.I.E.R3).

FAA-S-ACS-1, printed 7, PDF 12

Our scope is identification and suitability checking; this guide does not claim to cover a complete bolt-installation or torque project.

AM.I.E.S4 also covers materials: the handbook says aluminum-alloy sheets are marked with the specification number on approximately every square foot of material. Where used, the temper designation follows the alloy designation after a dash, as in 2024-T4.

FAA-H-8083-30B, General, printed 7-21, PDF 265 · FAA-H-8083-30B, General, printed 7-7, PDF 251

Set up a traceable identification sequence

The ACS safety appendix lists use of current maintenance and overhaul publications and procedures among the safety precautions the evaluator ensures you follow. Observation of safety precautions includes wearing safety glasses, hearing protection and any other required personal protective equipment (PPE).

FAA-S-ACS-1, printed A-3, PDF 67

Disregarding safety is not tolerated under the ACS and will result in a failure. If the task requires an action that would jeopardize safety, the evaluator will ask you to simulate that portion of the project.

FAA-S-ACS-1, printed A-3, PDF 67

Most aircraft hardware is identified by a specification number or trade name. Threaded fasteners and rivets use AN (Air Force-Navy), NAS (National Aircraft Standard) or MS (Military Standard) numbers.

FAA-H-8083-30B, General, printed 7-37, PDF 281

• Our bench workflow: read every legible head mark, record the full part number, identify the standard and compare the referenced configuration with the actual piece.
• When replacing hardware, a duplicate of the original should be used if possible; selecting a substitute requires extreme care and caution.
• Examine the markings on the bolt head to determine that each bolt is of the correct material. For bolt replacement, it is extremely important to use like bolts and in every case refer to the applicable maintenance instructions and illustrated parts breakdown.
• AC 43.13-1B says only hardware with traceability to an approved manufacturing process or source should be used. Hardware that is not traceable or is improperly altered may be substandard or counterfeit, because its physical properties cannot be substantiated. Care should be taken to ensure fasteners are approved by the FAA for the intended installation, repair or replacement.
• Our stop point: an unreadable mark or missing part-number suffix remains unresolved until the applicable parts data establishes identity and suitability.

FAA-H-8083-30B, General, printed 7-37, PDF 281 · FAA-H-8083-30B, General, printed 7-48, PDF 292 · AC 43.13-1B with Change 1, printed 7-5, PDF 317

Read bolt markings before choosing a replacement

• AN bolt-head code marks generally identify the manufacturer, material and whether the bolt is standard or special purpose.
• AC 43.13-1B adds that bolts with no markings are low strength.
• A close-tolerance NAS bolt has a raised or recessed triangle marking.
• AC 43.13-1B says not to substitute for close-tolerance fasteners without specific instructions from the aircraft manufacturer or the FAA. The same AC caution says care must be exercised with close-tolerance bolts in all critical applications, such as landing gear, control systems and helicopter rotary controls.
• Special bolts are made for particular applications, where like replacements are extremely important, and are usually identified by an S on the head.
• Our reference check: compare head marks with General Figure 7-19 and the exact part standard instead of inventing a material identity from appearance.
• Internal-wrenching MS-20004 through MS-20024 or NAS-495 bolts are high-strength steel parts suitable for tension and shear.
• An internal-wrenching bolt must be replaced with another internal-wrenching bolt; standard AN hex bolts and washers cannot substitute because they lack the required strength.
• In steel, the internal-wrenching bolt hole must be slightly countersunk for the head-to-shank radius; Dural applications require a special heat-treated washer for head bearing.
• Clevis bolts are used only for shear loads and never for tension.
• Jo-bolts should not be used where a loosened piece could be drawn into an engine intake.
• Aluminum-alloy bolts and nuts are not used where maintenance or inspection requires repeated removal.

FAA-H-8083-30B, General, printed 7-38, PDF 282 · FAA-H-8083-30B, General, printed 7-39, PDF 283 · FAA-H-8083-30B, General, printed 7-37, PDF 281 · AC 43.13-1B with Change 1, printed 7-5, PDF 317 · AC 43.13-1B with Change 1, printed 7-9–7-10, PDF 321, 322

Alloy-steel bolts smaller than No. 10-32 and aluminum-alloy bolts smaller than a quarter inch are not used in primary structures. Aluminum-alloy nuts may be used with shear-loaded cadmium-plated steel bolts on land airplanes, but not on seaplanes because of increased dissimilar-metal corrosion risk.

FAA-H-8083-30B, General, printed 7-38, PDF 282

Identify the nut and its locking restrictions

The handbook says no identifying marking or lettering appears on nuts; they can be further identified by their construction. For a self-locking nut, only the characteristic metallic luster or color of the aluminum, brass or insert can identify it.

FAA-H-8083-30B, General, printed 7-41, PDF 285

• Before replacing any nut with any other type, AC 43.13-1B says to refer to the aircraft manufacturer’s structural repair manual, the manufacturer’s engineering department or the FAA.
• AN310 identifies a castle nut; AN320 identifies a shallower, weaker castellated shear nut for shear-only applications such as drilled clevis bolts.
• AN315 and AN335 are plain hex nuts, AN316 is a plain check nut, and AN350 is a wing nut.
• Nut suffix letters and digits convey such details as material, size, thread pitch and right- or left-hand thread.
• Self-locking nuts are acceptable subject to manufacturer restrictions, but do not use them at joints that subject either the nut or the bolt to rotation.
• An antifriction bearing or control pulley may use a self-locking nut when the inner race is clamped to the support by the nut and bolt.
• AC 43.13-1B adds that self-locking nuts should not be used on turbine-engine airplanes where a loose nut, bolt, washer or screw could fall or be drawn into the engine air intake scoop. They also should not be used to attach access panels or doors, or to assemble parts that are routinely disassembled before or after each flight.
• For reused elastic stop nuts, check that the fiber retains locking friction and is not brittle; replace a nut that can be turned with the fingers.
• AC 43.13-1B says not to reuse a fiber or nylon locknut that cannot meet the minimum prevailing torque values in its Table 7-2.
• Do not tap the fiber locking insert, and do not install elastic stop nuts above the handbook’s 250°F limit because locking effectiveness is reduced.
• Self-locking nuts on engines and accessories may be used when the engine manufacturer specifies them.
• Friction-anchored clinch- or spline-type nuts are not acceptable in aircraft structures; sheet spring nuts, such as speed nuts, are used in non-structural locations and should be used only where originally used in the fabrication of the aircraft.

FAA-H-8083-30B, General, printed 7-42, PDF 286 · FAA-H-8083-30B, General, printed 7-45, PDF 289 · FAA-H-8083-30B, General, printed 7-45–7-46, PDF 289, 290 · FAA-H-8083-30B, General, printed 7-44, PDF 288 · AC 43.13-1B with Change 1, printed 7-11, PDF 323

After tightening an elastic stop nut, a rounded or chamfered bolt end must extend at least its full round or chamfer through the nut. Flat-ended bolts, studs and screws should extend at least one thirty-second of an inch through the nut. Bolts at least five-sixteenths of an inch in diameter with cotter-pin holes may be used with self-locking nuts only if those holes are free of burrs.

FAA-H-8083-30B, General, printed 7-44–7-45, PDF 288, 289 · FAA-H-8083-30B, General, printed 7-45, PDF 289

Match the washer to the function and bolt

• AN960 and AN970 plain washers provide bearing surfaces and can shim the assembly to obtain correct grip length.
• AN970 provides more bearing area than AN960 and is used under the head and nut on wood to prevent surface crushing.
• NAS143 and MS20002 washers serve NAS144 through NAS158 internal-wrenching bolts, with countersunk C versions seating the head-to-shank radius and plain versions under the nut.
• Shake-proof tab washers should be used only once because tabs tend to break on a second bend.
• Lock washers should never be used with primary- or secondary-structure fasteners or where failure could damage or endanger the aircraft or personnel.
• The same never-use list includes places where failure would permit a joint to open to the airflow, where the screw is subject to frequent removal, and where the washers are exposed to the airflow or subject to corrosive conditions.
• A lock washer against soft material should never be used without a plain washer beneath it to prevent gouging.

FAA-H-8083-30B, General, printed 7-46, PDF 290 · FAA-H-8083-30B, General, printed 7-47, PDF 291 · FAA-H-8083-30B, General, printed 7-46–7-47, PDF 290, 291

Identify screws by their standard and suffix legend

• AN509 and AN525 are structural-screw series with definite grip and shear strength equal to a bolt of the same size.
• AN515 roundhead machine screws have coarse threads, while AN520 roundhead screws have fine threads.
• Self-tapping screws should not replace standard screws, nuts, bolts or rivets.
• AN535 drive screws are not intended to be removed after installation.
• In the handbook’s NAS coding text, the basic NAS number identifies the part, but the dash numbers and suffix letters do not have standard meanings; refer to the specific NAS page in the Standards book for the legend.
• As a decoding illustration, AN501B-416-7 denotes the handbook’s brass fine-thread fillister-head screw with a quarter-inch diameter and a seven-sixteenths-inch length.
• Our check: do not transfer an AN screw’s suffix interpretation to an unrelated NAS or MS part without its own reference legend.

FAA-H-8083-30B, General, printed 7-66–7-67, PDF 310, 311 · FAA-H-8083-30B, General, printed 7-67, PDF 311 · FAA-H-8083-30B, General, printed 7-68, PDF 312

Measure grip length and report the identification

• Bolt grip length is the unthreaded shank length and should equal the thickness of the material being bolted.
• Slightly greater grip is permitted with washers under the head or nut; for plate nuts, the handbook calls for shims under the plate. AC 43.13-1B adds that the maximum combined height of washers that should be used is one-eighth of an inch.
• Bolts having damaged threads and rough ends are unacceptable.
• Our identification record gives the complete part number, observed head marks, reference used, material, thread information, measured grip where relevant and the application’s suitability conclusion.

FAA-H-8083-30B, General, printed 7-48, PDF 292 · FAA-H-8083-30B, General, printed 7-45, PDF 289 · AC 43.13-1B with Change 1, printed 7-5, PDF 317

Common identification mistakes

• Our checklist: avoid guessing identity from head shape alone, dropping a suffix, calling overall length grip length, or accepting a substitute merely because its threads fit.
• Keep identification separate from installation: after identifying a part, use its applicable maintenance instructions for torque, safetying and any further work. For safetying, AC 43.13-1B says not to reuse cotter pins or safety wire.

AC 43.13-1B with Change 1, printed 7-6, PDF 318

For examiner fees and planning, read the DME exam cost guide.

Related guides

• Aircraft Hardware and Materials Oral Exam Questions and Answers
• Torque on the A&P Practical: Wrench Use, Extensions and Values
• Safety Wire Practical Test: Double-Twist and Turnbuckles
• Sheet Metal Structures Oral Exam Questions and Answers
• A&P Practical Projects: What the DME Evaluates on the O&P

Sources

Primary sources checked October 20, 2026.

• FAA-S-ACS-1
• FAA-H-8083-30B, General
• AC 43.13-1B with Change 1
• FAA Mechanic Test Generator FAQs, updated May 22, 2023
• Order 8900.1, Vol. 5, Ch. 5, Sec. 11, CHG 929
• FAA sample oral and practical test

About this guide: drafted with AI from the FAA sources listed on this page and checked claim by claim against them. Not reviewed by an A&P mechanic or DME. How we make our guides