BOTTOM TAPS have a chamfer (lead) of 1–2 threads, the angle of the lead being around 18 degrees per side. They are used to produce threads close to the bottom of blind holes.
IMPORTANT NOTE ON TERMINOLOGY! In the U.K. bottom taps are often referred to as ‘plugs’. In North America second taps are often referred to as ‘plugs’! This can easily lead to confusion. To avoid problems when ordering it is best to use the terms bottom, second and taper.
Another variation is that second taps are sometimes referred to as ‘intermediate’, and taper taps can be called ‘firsts’.