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CARRIAGE BOLT

Description: This looks like a machine screw. It has a square end and is partially threaded, but also has a rounded head with no slot; directly beneath the head is a square shoulder.

Buying information: Carriage bolts are good for use in wood-to-wood connections. They come with either rolled or cut thread. The cut-thread type has the threads cut right into the bolt; the rolled kind has the threads pressed into the bolt shaft that results in the threaded section being a little thicker than the bare shank.

How-to hints: The cut-thread kind is generally preferred. In the smaller bolt sizes, rolled thread works okay, but in the large sizes the shank or smooth part of the bolt may be a bit loose in a hole large enough to pass the threaded end. The cut thread will be uniform.

To use a carriage bolt, drill a hole the diameter of the shank. Drop the bolt into the hole, then use a hammer to drive it in the rest of the way to seat the square neck in the hole. You then place a washer and screw a nut on the end of the bolt that protrudes. Since the head is locked into the wood it does not have to be restrained while the nut is turned home.

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