A screw is a shaft which has a groove on its surface. It is designed to hold objects in a certain alignment. There are different types of screw heads which have different applications such as Robertson, Slotted and Polydrive.
Well worth using for bending angle iron or flat bending on making "flat corners" that are hard to control with out crimping. with setting a good spacing for various width could also be used from thin up to very heavy bar stock.