BSPT (Taper)		BSPP (Straight)		ISO (Taper)		ISO (straight)
designation	Pipe Size	TPI	Tap Drill Size	Decimal inch	Tap Drill Size	Decimal inch	Tap Drill Size mm	Decimal inch	Tap Drill Size mm	Decimal inch
1/16 - 28		28	1/4	0.2500	F	0.2570	6.3mm	0.2480	6.5mm	0.256
1/8 - 28	6mm	28	21/64	0.3281	Q	0.3320	8.3mm	0.3268	8.5mm	0.335
1/4 - 19	8mm	19	7/16	0.4375	29/64	0.4531	11mm	0.4331	11.5mm	0.453
3/8 - 19	10mm	19	9/16	0.5625	37/64	0.5781	14.5mm	0.5709	15mm	0.591
1/2 - 14	15mm	14	23/32	0.7188	47/64	0.7344	18mm	0.7087	18.5mm	0.728
3/4 - 14	20mm	14	59/64	0.9219	61/64	0.9531	23.5mm	0.9252	24mm	0.945
1 - 11	25mm	11	1 11/64	1.1719	1 3/16	1.1875	29.5mm	1.1614	30.2mm	1.189
1 1/4 - 11	32mm	11	1 1/2	1.5000	1 17/32	1.5313	38mm	1.4961	39mm	1.535
1 1/2 - 11	40mm	11	1 47/64	1.7344	1 49/64	1.7656	44mm	1.7323	45mm	1.772
2-11	50mm	11	2 3/16	2.1875	2 15/64	2.2344	55.5mm	2.1850	56.5mm	2.224

Last Updated: 20 February 2015