Form general purpose Acme threads. These high-speed steel taps are for use on most metal and plastic. With a square shank, they're compatible with tap holders for drill presses and milling machines. Also known as tandem taps, these have an extended chamfer with two sets of chamfered cutting threads. Because these sets of threads have different shapes, reversing the tap for removal may cause damage to the workpiece and is not recommended. Use these taps with a rigid setup to tap through holes only.