Sutton Carbon Hand Taps, BSW, Bottoming Lead. A Bottom Tap is used after a taper lead tap and is suitable for creating threads close to the bottom of blind holes. Made from Tungsten Chrome Alloy these taps are ideal for routine maintenance, repair work and for rethreading where high accuracy and tolerance thread is not critical in general purpose applications, non-ferrous metals & plastics. Straight flute taps are only suitable for hand operations, tapping up to 1-1/2 x diameter.