Spiralock® taps are furnished with ramp angles as shown here. This is referred to as style "BT" for bottom tapping. When tapping from the opposite end of a through hole, you must specify Spiralock style "TT" (top tapping), which has the ramp angle facing the opposite direction.
Cold forming taps produce a thread by deforming material instead of removing it. The starting minor diameter is larger and must be held to a tighter tolerance than with standard taps to ensure the threads fill out properly. Forming taps are suitable for all ductile materials with an elongation value above 10%, such as aluminum, brass, copper, and mild steels. Lubrication with cutting oil is preferred.