A t-bolt, also referred to as a t-slot bolt, is a threaded fastener used in a machine's slot for holding. T-slot bolts are often made from steel, with their strength described in either grade or class. They may also include a coating, such as black oxide, for corrosion resistance or other benefits including lubricity. Tensile strength and hardness should be specified, along with thread fit. T-bolts typically have their length measured from beneath the head, and this includes both the threaded and unthreaded portions of the fastener's shank. T-bolts usually have a length from under head, thread length, screw size, and compatible slot width specified. While the head of a t-bolt is square or rectangular, it may have a specially designed neck or a smooth round one.