Chicago screws, which are also known as Chicago Fasteners, Chicago Bolts, Sex Bolts, Screw Posts, Tee-Nuts and Binding Posts, take the place of the permanently sewn on thread, and allow you to swap out different belt buckles with the same leather strap (or vice versa). The Chicago Screw functions by having two threaded pieces with flat heads on both ends, so they sit flush against the leather of the strap, with one piece screwing into the other to create a strong, reliable hold on the buckle.