TIGHTENING TORQUE VALUES FOR STEEL THREADED FASTENERS

Engineering

DATA SHEET 36

Standards

PAGE 2

2. All torque values

shown in customary (LB.FT) units represent values as described in NOTE 1 rounded to the

nearest multiple

of 5 or, in some cases, to the nearest whole number. All torque values shown in metric

(N.m) units are

rounded conversions that are estimated to be practical for the increments involved in

torque wrenches

calibrated in newton-metre units.

3. The torque values listed develop clamping forces that are based on material proof loads specified in SAE

Standard J429 in conjunction with the coefficient of friction value found to be characteristic of the H

coating. For Grades 5 and 8 cap screws, the clamping forces developed are 85+5% and 75+5% of proof loads

for coarse and fine threads respectively. For socket head and 12 point cap screws,the clamping forces

developed are 100+5% and 90+5% of proof loads for coarse and fine threads respectively.

4. The same torque values apply to both coarse and fine threaded fasteners as a result of the clamping

forces being approximately equal when calculated in accordance with NOTE 3. To illustrate, the proof

loads for Grade 8 fasteners with .750-10 and .750-16 threads are 40 100 and 44 800 lb respectively. The

clamping forces, determined by multiplying these proof loads by 0.85 and 0.75 respectively, are 34 100 lb

and 33 600 lb, which for all practical purposes are considered equal.

5. The torque values given apply while the fastener is being turned. After a joint is tightened, it may be

checked by trying to tighten it further, recognizing that the torque required to start further motion

will be about 10% higher than the specified value.