torquing inch-based bolts

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.

Approximate Torque Settings for Cadmium-plated Steel Bolts,
as received, not specially lubricated, in foot-pounds
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

 

Approximate Torque Settings for Unplated Steel Bolts,
as received, not specially lubricated, in foot-pounds
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

Torquing machine screws

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.

Grade 5, steel, not specially lubricated
Size Inch-pounds
6-32 16
6-40 18
8-32 30
8-36 31
10-24 43
10-32 49
X

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Copyright © 1999-2004 Sizes, Inc.  All rights reserved.
Last revised: 18 February 2004.