This tool is used in place of the standard 5/32" hex key that is furnished with your lathe or milling machine. The majority of adjustments on Sherline tools and accessories are made with this size hex key. Its large black plastic handle is more comfortable and provides better leverage than the shorter standard key. Also, because of its larger size, it is easier to spot on your workbench when you want to use it. This T-driver will quickly become your most often-used tool.