Tap			Pipe	
Thread		Drill		Dec.		Dia	TPI
1/16 NPT	C		0.242		
1/8 NPT		Q[R]		0.332		0.405	27
1/4 NPT		7/16		0.4375		0.540	18
3/8 NPT		9/16(37/64)	0.5625(0.5781)	0.675	18
1/2 NPT		45/64(23/32)	0.7031(0.7188)	0.840	14
3/4 NPT		29/32(59/64)	0.9062(0.9219)	1.050	14
1 NPT		1-9/64(1-5/32)	1.1406(1.1562)	1.315	11.5