Silicon Bronze Hex bolts. Tighten hex head cap bolts and screws with a socket or hex wrench. These imported fasteners are ideal for marine environments, especially where high amounts of torque must be applied. Bolts shorter than 4 in. will be full thread. 5 in. bolts may or may not be full thread. Bolts longer than 5 in. will have a shoulder. Threaded in imperial UNC thread.