Invented more than two thousand years ago, the screw has been used both as a simple machine and, more commonly now, as a fastener to hold two objects together. The latter usage is so widespread and universal that screws and screwdriver tools remain ever-present in every mechanical aspect of our modern lives. A simple and yet versatile fastener, the screw has been modified for different workspaces and work materials. Each screw can be divided broadly into two parts the shaft and the head. The shaft of the screw is a threaded cylinder that may or may not be tapered. The head allows the screw to be rotated, so it may be tightened or loosened as desired with a hand screwdriver.