Whats the correct torque?
A frequent question, but cannot be reduced to a simple answer or reference table. Many variables determine the correct answer – fastener surface finish, coating, plating, class of screw thread fit, etc. All variables must be taken into account to determine a realistic torque coefficient. Once calculated, check the result in a sample joint to measure clamp load induced from a given applied torque or breaking torque. Then back off an appropriate percentage. But remember that induced variances can be ±20% from a norm. Good reference information can be found in IFI’s Fastener Standards, Sixth Edition ($99.50 – U.S. & Canada; $145 – all other countries); and in An Introduction to the Design & Behavior of Bolted Joints by John Bickford, which is also available from IFI ($106 – U.S. & Canada; $126 – all other countries).
