What is a Joint Bolt?

J. Airman

A joint bolt is a cylindrical metal fastener used to connect two surface and hold them together. Most joint bolts are threaded at one end and have a fixed bolt head at the other end. A nut is often tightened onto the end of a joint bolt, with or without a washer, to secure the connection. Joint bolts are commonly used in conjunction with metal brackets or other forms of metal bracing to keep a joined section from separating. Joint connector bolts can be found making connections in cars, furniture, and even home construction.

Most joint bolts are threaded at one end and have a fixed bolt head at the other end.
Most joint bolts are threaded at one end and have a fixed bolt head at the other end.

Joint bolts are most likely to be used when both connecting surfaces are thin enough to bridge the distance between their outer edges with the bolt length. The joint bolt is usually inserted perpendicular to the joining surfaces so the fixed bolt end sits flush on one of the outer edges. Surfaces that are too thick for a joint bolt often require that a screw joint be driven into them to provide an anchor for the connection. An anchored screw joint is generally less desirable than that of a joint bolt because it is much less secure. Adding a lock washer to the joint bolt before the nut is threaded into place helps to prevent loose joints in the future.

Over-tightening a joint bolt can cause it to embed into one or both of the surface materials. Joint bolts will continue to tighten until the outer surfaces provide resistance or the last row of threads have been reached. The over-tightening technique is sometimes used by furniture and cabinet makers to shrink the length of joint bolts below the level of the surface and make them less visible. Wood putty can be applied to the newly created divots, and the ends of the joints bolts are completely hidden. Embedding and covering joint bolts makes it difficult to tighten or remove them in the future.

Selecting a quality compatible joint bolt for the job will ensure a secure connection. Bent or rusted joint bolts have decreased strength and can cause a joined edge or corner to misalign or become unstable. Joint bolts intended for outdoor use are coated in a thin layer of zinc in a process called galvanization. The zinc barrier helps to prevent the rust and corrosion that is common with exposure to weather. The nut and washer should also be galvanized if the fastener may come in contact with moisture.

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