Internal Dryseal Pipe Thread Tap Drill Sizes Recommendations

ANSI Hardware Design Guide and Charts
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The following are the recommended tap drill sizes for internal dryseal pipe threads.

Designation of Dryseal Pipe Threads: The standard Dryseal pipe threads are designated by specifying in sequence nominal size, thread series symbol, and class: Examples:1⁄8-27 NPTF-1; 1⁄8-27 PTF-SAE SHORT; and 3⁄8-18 NPTF-1 AFTER PLATING.

Internal Dryseal Pipe Thread

Nominal Size	Probable Drill Oversize Cut (Mean)	Taper Pipe Thread				Straight Pipe Thread
		Minor Diameter At Distance		Drill Size		Minor Diameter		Drill Size
		L1 From Large End	L1 + L3 From Large End	Without Reamer	With Reamer	NPSF	NPSI	Drill Size
1/16 - 27	0.0038	0.2443	0.2374	“C” (0.242)	“A” (0.234)	0.2482	0.2505	“D” (0.246)
1/8 - 27	0.0044	0.3367	0.3298	“Q” (0.332)	21/64 (0.328)	0.3406	0.3429	“R” (0.339)
1/4 - 18	0.0047	0.4362	0.4258	7/16 (0.438)	27/64 (0.422)	0.4422	0.4457	7/16 (0.438)
3/8 - 18	0.0049	0.5708	0.5604	9/16 (0.562)	9/16 (0.563)	0.5776	0.5811	37/64 (0.578)
1/2 - 14	0.0051	0.7034	0.6901	45/64 (0.703)	11/16 (0.688)	0.7133	0.7180	45/64 (0.703)
3/4 - 14	0.0060	0.9127	0.8993	29/32 (0.906)	57/64 (0.891)	0.9238	0.9283	59/64 (0.922)
1 - 11 1/2	0.0080	1.1470	1.1307	19/64 (1.141)	1 1/8 (1.125)	1.1600	1.1655	15/32 (1.156)
1 1/4 - 111 2	0.0100	1.4905	1.4742	13 1/64 (1.484)	1 15/32 (1.469)	…	…	…
1 1/2 - 11 1/2	0.0120	1.7295	1.7132	1 23/32 (1.719)	1 45/64 (1.703)	…	…	…
2 - 11 1/2	0.0160	2.2024	2.1861	2 3/16 (2.188)	2 11/64 (2.172)	…	…	…
2 1/2 - 8	0.0180	2.6234	2.6000	2 39/64 (2.609)	2 37/64 (2.578)	…	…	…
3 - 8	0.0200	3.2445	3.2211	3 15/64 (3.234)	3 13/64 (3.203)	…	…	…