Taper pipe thread

Nominal diameter	Pitch (reference)	External thread diameter at the gauge plane			Position of the gauge plane a	Tapping drill diameter for the internal thread
Nominal diameter	Pitch (reference)	Major diameter	Pitch diameter d₁	Minor diameter d₂	Position of the gauge plane a	Tapping drill diameter for the internal thread

Notes

The tapping drill diameter is a reference value not given in JIS B 0203; it is a guide for cutting the internal thread with a tap. Sizes 4 and above are left blank because tool manufacturers do not list them either.
References