⚙️ Aviation Hardware Reference Chart
Common AN/MS bolt sizes, wrench sizes, thread specifications, and typical aviation usage notes for aircraft mechanics.
AN Bolt / Screw Size Reference
AN (Air Force-Navy) bolts use the designation AN3 through AN20, where the number indicates the diameter in 1/16" increments. Example: AN3 = 3/16" diameter, AN4 = 1/4" diameter.
| AN Number | Diameter | Thread (UNF) | Wrench Size | Drill (Clearance) | Typical Use |
|---|---|---|---|---|---|
| AN3 | 3/16" | 10-32 | 5/16" | #10 (0.194") | Control cable fittings, light brackets, inspection panels |
| AN4 | 1/4" | 1/4-28 | 7/16" | F (0.257") | General airframe hardware, hinges, secondary structure |
| AN5 | 5/16" | 5/16-24 | 1/2" | O (0.316") | Engine mounts, structural brackets, moderately loaded joints |
| AN6 | 3/8" | 3/8-24 | 9/16" | W (0.386") | Primary structure, wing attach fittings, landing gear brackets |
| AN7 | 7/16" | 7/16-20 | 5/8" | 29/64" | Heavy structural applications, engine mounts |
| AN8 | 1/2" | 1/2-20 | 3/4" | 33/64" | Main landing gear attachments, heavy primary structure |
| AN10 | 5/8" | 5/8-18 | 15/16" | 41/64" | Main spar fittings, wing carry-through structures |
| AN12 | 3/4" | 3/4-16 | 1-1/8" | 49/64" | Heavy structural bolts, engine mount main bolts |
Common AN/MS Nut Reference
| Part Number | Type | Size | Notes |
|---|---|---|---|
| AN310 | Castle Nut | AN3–AN20 range | Used with AN cotter pins for positive locking on primary control systems. Do not substitute with AN320. |
| AN320 | Shear Castle Nut | AN3–AN16 range | Lighter than AN310. Used in shear (non-tension) applications. Not interchangeable with AN310 in tension applications. |
| AN315 / AN335 | Plain Hex Nut | Various | Requires safety wiring or cotter pin for positive lock. Standard aircraft hex nut. |
| MS21042 | Self-Locking (all-metal) | Various (replaces AN365) | High-temperature self-locking nut. Can be reused per AMM guidance, but replace if locking torque is insufficient. |
| AN365 / MS21045 | Self-Locking (nylon insert) | Various | Nyloc-type nut. Not approved above 250°F (121°C). Replace after removal — nylon insert loses effectiveness. |
| AN363 | Self-Locking (light) | Various | Light-duty self-locking nut for low-vibration, non-critical applications. |
Washer Reference
| Part Number | Type | Notes |
|---|---|---|
| AN960 | Flat Washer (standard) | Most common aircraft washer. Used under bolt heads and nuts. Size coded to bolt (AN960-4 for AN4, etc.). |
| AN970 | Flat Washer (large OD) | Larger outside diameter for use with wood or soft material to distribute load. Less common on metal structure. |
| AN935 | Lock Washer (split ring) | Provides locking through spring tension. Not used in primary structure — mostly on electrical equipment and instruments. |
| AN936 | Lock Washer (tooth) | External or internal tooth for electrical bonding and panel screws. Provides ground path as well as locking. |
| MS20002 | Countersunk Washer | Used with countersunk bolts to fill the countersink and provide a bearing surface for the nut. |
UNF vs UNC Threads
Aircraft hardware primarily uses UNF (Unified National Fine) threads, which have more threads per inch than UNC (coarse). Fine threads are preferred in aviation for better resistance to vibration loosening and better torque-to-clamping force ratios. UNC threads appear on some structural applications where stripped threads are a concern. Never mix UNF and UNC hardware.
Bolt Grip Length
Grip length is the unthreaded shank portion of the bolt. Bolts should be selected so the grip length matches the material thickness being clamped. Threads should not be in the shear plane. The correct grip length is when 1–3 threads are visible beyond the nut when fully torqued. Using washers to adjust effective grip is acceptable within AMM limits.