SIZE	THREADS per INCH	TAP DRILL SIZE (mm)
1/8"	27	9.00
1/4"	18	11.50
3/8"	18	15.00
1/2"	14	18.50
3/4"	14	23.75
1"	11.5	30.00
1.1/4"	11.5	39.00
1.1/2"	11.5	45.00