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Speedmart Tech Support

Torque Accuracy
SpeedMart Tech Team

Torque Accuracy on Fasteners
Screw threads appear to be a simple concept yet much confusion and inconsistency exist regarding torque values. The mechanics of the screw thread are actually very complex and have numerous interacting variables. Sliding friction is affected by materials (like steel or aluminum on titanium), surface roughness, bearing area, material hardness, lubrication and so on.

Accuracy: Tightening is not an accurate science, look at the preloading accuracy published in the "Machinery's Handbook, 25th Edition, page 1404"

Method

Accuracy

By Feel

+/- 35%

Torque Wrench

+/- 25%

Turn-of-nut

+/- 15%

Preload washers

+/- 10%

Bolt elongation

+/- 3%

Strain gauges

+/- 1%

 

 

Torque Limits for American Size Bolts in Tension
(For bolts in shear reduce the values shown below by 30-40%)

Non-lubricated

Lubricated

Torque

Torque

Torque

Torque

Bolt Size

Min.

Max.

Bolt Size

Min.

Max.

5/16-18

80 in lbs

90 in lbs

5/16-18

72 in lbs

81 in lbs

5/16-24

120 in lbs

145 in lbs

5/16-24

108 in lbs

130 in lbs

3/8-16

160 in lbs

185 in lbs

3/8-16

144 in lbs

148 in lbs

3/8-24

200in lbs

250 in lbs

3/8-24

180 in lbs

225 in lbs

7/16-14

235 in lbs

255 in lbs

7/16-14

211 in lbs

229 in lbs

7/16-20

520 in lbs

630 in lbs

7/16-20

468 in lbs

567 in lbs

-13

400 in lbs

480 in lbs

-13

360 in lbs

432 in lbs

-20

770 in lbs

950 in lbs

-20

693 in lbs

855 in lbs

Recommended Torque Spec's for Titanium Fasteners
Use torque values specified by your equipment manufacture, when available. For titanium fasteners the torque values are listed below. We recommend anti-seize or moly paste be applied to the threads

The importance of correct application cannot be overemphasized. Undertorque can result in unnecessary wear of nuts and bolts as well as the parts they hold together. When insufficient pressures are applied, uneven loads will be transmitted throughout the assembly which may result in excessive wear or premature failure due to fatigue. Overtorque can be equally damaging because of failure of the bolt or nut from overstressing the thread areas.