As a rule, when a bolt is installed, the nut (over a washer) should be turned and not the bolt's head. Unless a torque wrench is used the tendency is to undertighten large bolts and overtighten small ones. Suggested torques are given below. These suggestions do not apply if the bolt or nut has been specially lubricated. In all cases, the specifications of the manufacturer of the equipment should be preferred to tables of approximations like these.
Bolt grade | Bolt diameter in inches | |||||||||
---|---|---|---|---|---|---|---|---|---|---|
¼ | 5/16 | 3/8 | 7/16 | ½ | 9/16 | 5/8 | ¾ | 7/8 | 1 | |
SAE 2 | 4.6 | 9 | 15 | 24 | 36 | 50 | 69 | 117 | 184 | 273 |
SAE 3 | 6.9 | 14 | 24 | 38 | 57 | 82 | 113 | 198 | 317 | 477 |
SAE 5 | 7.5 | 15 | 25 | 40 | 59 | 83 | 114 | 196 | 309 | 459 |
SAE 6, SAE 7 |
9.7 | 19 | 34 | 55 | 83 | 120 | 166 | 291 | 469 | 710 |
SAE 8 | 10.5 | 21 | 37 | 60 | 90 | 130 | 180 | 316 | 509 | 769 |
Socket Head Cap Screws |
12.7 | 25 | 45 | 72 | 109 | 157 | 217 | 381 | 615 | 929 |
Bolt grade | Bolt diameter in inches | |||||||||
---|---|---|---|---|---|---|---|---|---|---|
¼ | 5/16 | 3/8 | 7/16 | ½ | 9/16 | 5/8 | ¾ | 7/8 | 1 | |
SAE 2 | 5.8 | 11 | 19 | 30 | 44 | 63 | 86 | 146 | 230 | 341 |
SAE 3 | 8.6 | 17 | 30 | 47 | 71 | 102 | 141 | 247 | 396 | 596 |
SAE 5 | 9.4 | 18 | 31 | 49 | 74 | 104 | 142 | 245 | 386 | 574 |
SAE 6, SAE 7 |
12.2 | 24 | 43 | 69 | 104 | 149 | 207 | 364 | 587 | 887 |
SAE 8 | 13.2 | 26 | 46 | 74 | 113 | 162 | 225 | 395 | 636 | 962 |
Socket Head Cap Screws |
14.1 | 28 | 50 | 80 | 121 | 174 | 241 | 424 | 683 | 1033 |
Experiment is the best way of determining torque values for small fasteners. Pick at least 7 sets of parts at random and assemble them, torquing the fastener until it fails. (The values at failure should fall within a fairly narrow range; if they don't, something is amiss with the parts, the torque wrench, or your technique.) Find the average failure value, then take 65% of it. The following table gives a rough idea of values to be expected.
Size | Inch-pounds |
---|---|
6-32 | 16 |
6-40 | 18 |
8-32 | 30 |
8-36 | 31 |
10-24 | 43 |
10-32 | 49 |
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Copyright © 1999-2004 Sizes, Inc. All rights reserved.
Last revised: 18 February 2004.