Countersunk bolts are used when a smooth surface is required. Common applications include bridge decking, walkways, and railing.
Manufacturing
Portland Bolt manufactures countersunk bolts from 1/2″ diameter through 1-1/2″ diameter in most ASTM, AASHTO, and SAE specifications, including A307 Grade A, A449, and F3125 Grade A325. Countersunk bolts have a head angle of approximately 80 degrees. Special tooling can be created to produce nonstandard head dimensions or bolt heads with your company’s name and/or logo.
Slots in Countersunk Bolts
Countersunk heads can include a machined slot, forged slot, or no slot whatsoever. A slot allows the head to be held securely with a flathead screwdriver while the nut is assembled onto the bolt. Forged slots measure 1/8″ wide x 1/8″ deep x 5/8″ long. Machined slot dimensions are listed in the table below.
Standard Thread Length
Bolt lengths ≤ 6″: Thread length = (2 X diameter) + 1/4″
Bolt lengths > 6″: Thread length = (2 X diameter) + 1/2″
Note: Most stock hex bolts longer than 12″ in length will have 6″ of thread.
Countersunk Dimensions
| Bolt Diameter | D | F | H | J | S | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| Body Diameter | Head Diameter | Head Height | Slot Width | Slot Depth | ||||||
| Max | Max Edge Sharp | Min Edge Sharp | Absolute Min Rounded | Max | Min | Max | Min | Max | Min | |
| 1⁄2 | 0.515 | 0.935 | 0.905 | 0.845 | 0.269 | 0.233 | 0.106 | 0.091 | 0.103 | 0.068 |
| 5⁄8 | 0.642 | 1.169 | 1.132 | 1.066 | 0.336 | 0.292 | 0.113 | 0.116 | 0.137 | 0.091 |
| 3⁄4 | 0.768 | 1.402 | 1.357 | 1.285 | 0.403 | 0.349 | 0.149 | 0.131 | 0.171 | 0.115 |
| 7⁄8 | 0.895 | 1.637 | 1.584 | 1.511 | 0.470 | 0.408 | 0.167 | 0.147 | 0.206 | 0.138 |
| 1 | 1.022 | 1.869 | 1.810 | 1.735 | 0.537 | 0.466 | 0.188 | 0.166 | 0.240 | 0.162 |
| 11⁄8 | 1.149 | 2.104 | 2.037 | 1.962 | 0.604 | 0.525 | 0.196 | 0.178 | 0.257 | 0.173 |
| 11⁄4 | 1.277 | 2.337 | 2.262 | 2.187 | 0.671 | 0.582 | 0.211 | 0.193 | 0.291 | 0.197 |
| 13⁄8 | 1.404 | 2.571 | 2.489 | 2.414 | 0.738 | 0.641 | 0.226 | 0.208 | 0.326 | 0.220 |
| 11⁄2 | 1.531 | 2.804 | 2.715 | 2.640 | 0.805 | 0.698 | 0.258 | 0.240 | 0.360 | 0.244 |
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Dimensions per ASME B18.5 1990 (R 1998) | ||||||||||