Shape Of The Bolt

The countersunk head is often used in situations where a smooth surface is desired, as it can be screwed flush into the material. Round heads are also suitable for screwing into parts, but square heads can offer greater tightening force, however they may be too large for some applications. To prevent loosening due to vibrations, some bolts feature holes in both the head and rod. Thin-waisted bolts may be used for variable force connections. High-strength bolts used in steel structures can be larger and come in various sizes. Special bolts include T-slot bolts for machine tool fixtures, anchor bolts for securing machines to the ground, and U-bolts. Studs for welding have threads on one end and can be welded onto parts.