Standard NPT Tap Drill Sizes
NPT Size	Tap Drill Size (in.)	Decimal Equivalent (in.)
1/16 - 27	"C"	0.242
1/8 - 27	"Q"	0.332
1/4 - 18	7/16	0.438
3/8 - 18	9/16	0.562
1/2 - 14	45/64	0.703
3/4 - 14	29/32	0.906
1.0 - 11•1/2	1•9/64	1.141
1•1/4 - 11•1/2	1•31/64	1.484
1•1/2 - 11•1/2	1•23/32	1.719
2.0 - 11•1/2	2•3/16	2.188
2•1/2 - 8	2•39/64	2.609
3.0 - 8	3•15/64	3.234