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AN8-31
Aeronautical Standard Machine Bolt
Description
Hex head aircraft bolts are made of high-strength type 4037 or 8740 alloy steel (type 8740 is most commonly used). The bolts are centerless ground and threaded after heat treatment. Minimum tensile strength 125,000 PSI. Cadmium plated per specification QQ-P-416A, Type II, Class 3. Available with shank drilled for cotter pin or undrilled for stop nut application, and with or without drilled head for safety wire. Specify bolts to have undrilled shank by adding letter "A" after the dash number. For bolts with drilled head add letter "H" after the AN number. See illustrated examples. "C" represents Type 431 Stainless Steel (contains iron which is magnetic). The length of AN aircraft bolts is measured from under the head to the end of the shank. The "grip" is the unthreaded portion of the shank. See table for conversion of length and/or grip to proper AN callout. Note: Drilled bolts listed above are drilled shank only. To order drilled head only or both drilled head and shank bolts, please use our AN Bolt Selector by clicking the link below
Specifications
| Distance From Head Largest Bearing Surface To Shank Hole Center | 3.031 inches first hole and 3.063 inches first hole |
|---|---|
| Fastener Length | Between 3.203 inches and 3.250 inches |
| Features Provided | Finished head |
| Grip Length | 2 7/16, Between 2.522 inches and 2.554 inches |
| Hardness Rating | 26.0 rockwell c and 32.0 rockwell c |
| Head Height | Between 0.265 inches and 0.297 inches |
| Head Style | Hexagon Head |
| Material | Steel |
| Min. Tensile Strength (psi) | 125000 pounds per square inch |
| Nominal Length | 3 7/32 |
| Shank Unthreaded Hole Diameter | 0.106 inches first hole and 0.116 inches first hole |
| Surface Treatment | Cadmium or dichromate |
| Thread Class | 3a |
| Thread Diameter | 0.500 |
| Thread Direction | Right-hand |
| Thread Length | 0.681 |
| Thread Qty | 20 |
| Thread Qty Per Inch (tpi) | 20 |
| Thread Series | UNF |
| Thread Series Designator | Unf (fine thread) |
| Thread Size | 1/2 |
| Width Between Flats | Between 0.740 inches and 0.752 inches |
Cross-reference
No interchangeable or dimensionally similar parts are on record for AN8-31. Try the cross-reference lookup to search by a different part number.
Catalog data updated 2026-07-05. Report a data error