What is the difference between a tap bolt and a cap screw?

A tap bolt is (typically) a fully threaded hex bolt, while a cap screw is (typically) a hex head bolt that will be installed by turning the head of the bolt (screw) instead of tightening it with a nut. Usually cap screws are being threaded into something (a piece of machinery for example), rather than being used with a nut. A cap screw is not necessarily fully threaded unless you order it that way. Cap screws will follow a standard thread length formula as follows:

Standard Thread Length

For cap screws 6″ or less in length, thread length will be (2 X diameter) + 1/4″

For cap screws longer than 6″, thread length will be (2 X diameter) + 1/2″

To summarize, a bolt is installed by turning a nut, while a screw it installed by turning the head of the fastener.  A tap bolt implies that that fastener is fully threaded.

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2 comments

    Good explanation, however there is a major difference between a tap bolt and a hex cap screw. The HCS has a built in washer on the underside of the head and provides some relief from the points on the head making contact with the surface. Although a tap bolt is fully threaded, there is no washer face and the points make direct contact with the surface

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