A carriage bolt, also known as a plow bolt or a coach bolt, is a type of threaded fastener designed to be primarily used with wood, though can be used to fasten metal components. Timber is often secured together using carriage bolts during construction of homes and outdoor decks. They are commonly used in chain link fences, patio furniture, machinery assembly, and in cars and trucks.

The design of a carriage bolt includes a large round, domed head with a threaded bolt below it. The head is typically at least twice the diameter of the bolt shaft, and usually does not have slots for a screwdriver or other driving device. Underneath the head, there is a square fitting that grips the wood as the bolt is placed and fastened, keeping it from twisting or turning and otherwise maintaining a snug fit. Since the square fitting keeps the bolt from turning, carriage bolts are a good choice for situations in which the head of the bolt cannot be easily accessed. In a variation on the basic carriage bolt, the square fitting under the rounded head is replaced with ribbing that holds the bolt in place when it is used with other metal components. Like other bolts, the carriage bolt is designed to be used with a nut that secures it in place.

Typically, carriage bolts are used in pre-drilled holes; this is necessary, in most cases, because the bolt cannot be driven in by its round, smooth head. The square fitting that holds the bolt in place means that the nut can be tightened firmly, however, creating a solid fit. Often, the shaft of the bolt is smooth immediately under the fitting, as this area is completely within the material being joined, and therefore does not need to be threaded.

When assembling homes, cars or machinery, strength is of the utmost importance. A carriage bolt made of 6Al-4V titanium is 3 and a half times stronger than a similar bolt made of stainless steel. It is not only stronger, but it is also 44% lighter and will remain corrosion free in the natural environment, making it the perfect “get it and forget it” material for any structural fastener such as a carriage bolt.