Screw Torques

Let's analyze screws. For a given screw size, material and tapped hole, work out tensile strength, installation torque, and minimum thread engagement.

This page uses JavaScript for the analysis. For data tables, and the GNU public license, look at the JavaScript source code. This is a work in progress. I think the torques are correct, but I need to do more testing.

If it matters, double check my results by hand. You can print this page out to get a work sheet suitable for mark-up.

Screw Information

Screw...
Thread type:		Metric ISO, inch UNC and inch UNF are standard screws, stocked by fastener vendors. Metric fine and inch UN are weird sizes for which screws normally are not available. The taps often are. Some of these threads are used on panel mounted controls.
Thread:
Material:
Friction Factor:		From Faires, unlubricated: 0.2, lubricated: 0.15. Screw friction factor is a fun subject. Google it.
Loading:	% of yield or proof stress	75% is a good number for screws that may be removed and re-used. If the bolt will not be re-used, try 90%.
Inside diameter:		Hollow screw? 0=No.
Tapped hole...
Material:

Input Notes

When prompted for a length, you can enter fractions. You cannot enter fractions greater than one, i.e. 1-1/4. I need to work on this. The dimension 5/4 will work.

References

Bickford: Handbook of Bolts and Bolted Joints -- edited by John H. Bickford and Sayed Nassar. -- Marcel Dekker
Faires: Machine Design Fourth Edition -- Virgil M. Faires -- MacMillan Company
Machinery: Machinery's Handbook 26th Edition -- Eric Oberg, Franklin D. Jones, Holbrook L. Horton, Henry H. Ryffell -- Industrial Press
Matweb.com: Online materials reference
NASA: Fastener Design Manual, NASA Reference Publication 1228, March 1990, Richard T. Barret

Screw Torques

Screw Information

Dammit!

Input Notes

References

JavaScript