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Internal Dryseal Pipe Thread Tap Drill Sizes Recommendations

ANSI Hardware Design Guide and Charts
Fluids Flow Engineering

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
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)

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