Did you know that bolts and other threaded fasteners vary in strength, tolerances and design? When you remove old bolts, you need to select the correct replacements to ensure proper fit and clamping force.

Bolts vary by grade, which indicates both the material and the tensile strength. For fractional inch bolts, the grade is shown on the head by a series of raised marks. For metric bolts, the grade is shown by a raised number. Other symbols, letters, and numerals may also be used to indicate specific properties. Learn to identify the type of bolts and the grade — and don’t inter-mix or substitute them.

Some bolts and nuts have flanged heads, which replace separate washers. Always use either a flanged head bolt and nut or a bolt and nut with a separate pair of washers to distribute the clamping load over a larger area and avoid stress concentrations and gouging of the clamped surfaces.

And never re-use old fasteners — they already have been stretched under load and cannot be tightened again without risking failure.

This feature offers a variety of short tips and facts about apparatus specifications, maintenance and testing. Submissions of 150 words or less are welcome from our readers, subject to editing. Send them to Senior Editor Chris Cavette at cavettes@ix.netcom.com