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Torque vs. Direct Tension Indicators
Tightening Bolts Bolts are often tightened by applying torque to the head or nut, which causes the bolt to stretch. The elongation results in bolt tension or pre-load,
which is the force that holds the joint together. Torque is relatively easy to measure with a torque-wrench, so it is the most frequently used indicator of bolt tension.
Unfortunately, a torque-wrench does not measure bolt tension accurately, usually only about +/- 30%, because it does not take friction into account. The friction depends on bolt, nut,
washer-material, plating, surface smoothness, machining accuracy, degree of lubrication and the number of times a bolt has been tightened. Fastener manufacturers often provide information
for determining torque requirements for tightening various bolts, accounting for friction and other effects. However, in field applications, this information is often not available,
practical or administered poorly.
Size range
SmartBolts? are available in bolts ranging from 7/16" (M10) to 1 1/4" (M32).
Patents
Products are patented in the U.S. and Canada, and other patents are pending.
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