Friction Grip Bolt

A friction grip bolt is a high strength structural bolt used in joints that rely on friction between the connected plates. It is tightened to a high preload so the joint does not slip under load.

These bolts are used in steelwork connections such as bridges and heavy frames. They are matched with a nut and usually two hardened washers, one under the head and one under the nut. Installation often needs a torque wrench or a load indicating device to reach the required tension.

Hot dip galvanising gives a thick zinc coating that suits outdoor and corrosive environments. Plain finish has no added coating and is often used where the joint will be painted or where corrosion is not a concern. Zinc based coatings are also available for moderate protection.

Friction grip bolts are often made in alloy steel or high strength carbon steel. The material is chosen for its ability to hold a high preload without yielding.

This is a general guide to checking this kind of part. It says nothing about any supplier's parts.

Ask for a mill test certificate that shows the chemical composition and mechanical properties. On receipt, check the bolt markings, the condition of the threads and the coating thickness if galvanised. Also check that the washers and nuts match the bolt grade.