The type of bolt which has a coarse thread, a smooth round head and a black rough finish is the:

• A. Stove bolt
• B. Carriage bolt
• C. Lag bolt
• D. Stud bolt

Answer: (B)

A smooth round head with a square shoulder under the head and coarse threads is the telltale sign of a carriage bolt. The rounded head sits flush in a wooden surface, and the square neck fits into a recess so the bolt won’t turn when you tighten a nut on the other side. The coarse threads bite into wood, giving a strong hold, and a black oxide rough finish is common on these bolts.

This differs from lag bolts, which have hex heads and are driven with a wrench into wood; and from studs, which are threaded rods without a head for two-sided attachment. Some catalogs use “stove bolt” as a synonym for carriage bolt, but the round head with a square underhead is the key identification.