Tap size	Threads per Inch	Drill size for tapererd pipe without using reamer	Drill size using tapered pipe reamer	Drill size for straight pipe thread
1/16	27	D	15/64	1/4
1/8	27	Q	21/64	11/32
1/4	18	7/16	27/64	29/64
3/8	18	37/64	9/16	37/64
1/2	14	23/32	11/16	23/32
3/4	14	59/64	57/64	15/16
1	11.5	1-5/32	1-1/8	1-11/64
1-1/4	11.5	1-1/2	1-15/32	1-33/64
1-1/2	11.5	1-47/64	1-23/32	1-3/4
2	11.5	2-7/32	2-3/16	2-7/32