Recommended tap drill sizes (for approx. 75% thread)
INCH SIZES - NATIONAL COARSE ---------------------------- TAP DRILL SIZE SIZE ---------------------------- #1-64 #53 #2-56 #51 #3-48 5/64" #4-40 #43 #5-40 #38 #6-32 #36 #8-32 #29 #10-24 #25 #12-24 #17 1/4-20 #7 5/16-18 F 3/8-16 5/16 7/16-14 U 1/2-13 27/64 9/16-12 31/64 5/8-11 17/32 3/4-10 21/32 7/8-9 49/64 1"-8 7/8 1-1/8-7 63/64 1-1/4-7 1-7/64 1-1/2-6 1-11/32 1-3/4-5 1-35/64 2"-4-1/2 1-25/32 ---------------------------- |
INCH SIZES - NATIONAL FINE ---------------------------- TAP DRILL SIZE SIZE ---------------------------- #0-80 3/64" #1-72 #53 #2-64 #50 #3-56 #46 #4-48 #42 #5-44 #37 #6-40 #33 #8-36 #29 #10-32 #21 #12-28 #15 1/4-28 #3 5/16-24 I 3/8-24 Q 7/16-20 W 1/2-20 29/64 9/16-18 33/64 5/8-18 37/64 3/4-16 11/16 7/8-14 13/16 1"-14 15/16 1-1/8-12 1-3/64 1-1/4-12 1-11/64 1-1/2-12 1-27/64 1-3/4-12 1-43/64 2"-12 1-59/64 ---------------------------- |
TAPER PIPE SIZES - NPT ---------------------------- TAP DRILL SIZE SIZE ---------------------------- 1/8-27 R 1/4-18 7/16 3/8-18 37/64 1/2-14 23/32 3/4-14 59/64 1"-11-1/2 1-5/32 1-1/4-11-1/2 1-1/2 1-1/2-11-1/2 1-47/64 2"-11-1/2 2-7/32 2-1/2-8 2-5/8 3"-8 3-1/4 3-1/2-8 3-3/4 4"-8 4-1/4 ---------------------------- |
STRAIGHT PIPE SIZES - NPS ---------------------------- TAP DRILL SIZE SIZE ---------------------------- 1/8-27 S 1/4-18 29/64 3/8-18 19/32 1/2-14 47/64 3/4-14 15/16 1"-11-1/2 1-3/16 1-1/4-11-1/2 1-33/64 1-1/2-11-1/2 1-3/4 2"-11-1/2 2-7/32 2-1/2-8 2-21/32 3"-8 3-9/32 3-1/2-8 3-25/32 4"-8 4-9/32 ---------------------------- |
Recommended tap drill sizes (for approx. 75% thread)
METRIC COARSE SIZES ---------------------------- TAP DRILL SIZE SIZE ---------------------------- 1mm x .25 .75mm 1.1 x .25 .85 1.2 x .25 .95 1.4 x .3 1.1 1.6 x .35 1.25 1.7 x .35 1.3 1.8 x .35 1.45 2 x .4 1.6 2.2 x .45 1.75 2.5 x .45 2.05 3 x .5 2.5 3.5 x .6 2.9 4 x .7 3.3 4.5 x .75 3.7 5 x .8 4.2 6 x 1 5 7 x 1 6 8 x 1.25 6.8 9 x 1.25 7.8 10 x 1.5 8.5 11 x 1.5 9.5 12 x 1.75 10.2 14 x 2 12 16 x 2 14 18 x 2.5 15.5 20 x 2.5 17.5 22 x 2.5 19.5 24 x 3 21 27 x 3 24 30 x 3.5 26.5 33 x 3.5 29.5 36 x 4 32 39 x 4 35 ---------------------------- |
METRIC FINE SIZES ---------------------------- TAP DRILL SIZE SIZE ---------------------------- 4 mm x .35 3.6mm 4 x .5 3.5 5 x .5 4.5 6 x .5 5.5 6 x .75 5.25 7 x .75 6.25 8 x .5 7.5 8 x .75 7.25 8 x 1 7 9 x 1 8 10 x .75 9.25 10 x 1 9 10 x 1.25 8.8 11 x 1 10 12 x .75 11.25 12 x 1 11 12 x 1.5 10.5 14 x 1 13 14 x 1.25 12.8 14 x 1.5 12.5 16 x 1 15 16 x 1.5 14.5 18 x 1 17 18 x 2 16 20 x 1 19 20 x 1.5 18.5 20 x 2 18 22 x 1 21 22 x 1.5 20.5 22 x 2 20 24 x 1.5 22.5 24 x 2 22 26 x 1.5 24.5 27 x 1.5 25.5 27 x 2 25 28 x 1.5 26.5 30 x 1.5 28.5 30 x 2 28 33 x 2 31 36 x 3 33 39 x 3 36 ---------------------------- |
Suggested Drill Sizes |
|||
PG7 |
29/64" |
11.40mm |
|
PG9 |
9/16" |
14.00mm |
|
PG11 |
11/16" |
17.25mm |
|
PG13.5 |
49/64" |
19.00mm |
|
PG16 |
27/32" |
21.25mm |
|
PG21 |
1.5/64" |
26.75mm |
|
PG29 |
1.27/64" |
35.50mm |
|
PG36 |
45.50mm |
||
PG42 |
52.50mm |
||
PG48 |
57.75mm |
For Metric sizes only. Diameter of thread minus the pitch equals
the tap drill size.
eg. M6 x 1
6 - 1 = 5mm
and you thought metric was difficult ;-)
Thanks to Jay Steinbuchel of Barksdale Control Products for the following:
This works for all 75% threads, not just metric.
For example, the tap drill for 3/8-16 is 5/16.
The pitch is 1/16". (1 / threads per inch = inches per thread)
3/8 - 1/16 = 5/16.
For other sizes that don't work out so nicely, just use the closest drill size.
Based on a 100% of thread as per ANSI to calculate tap drill size for acme taps.
the magic formulastep 1
1 Divided by TPI ( threads per inch)
step 2
subtract this amount from the OD. for pitches 10 and greater always add .005" for the drill size for pitches less than 10 TPI take the amount from step 1 and multiply x.05 ( 5 %) and add this to the drill size. This is for 95% to 100% threads.eg 1/2-10
1/10 = .100 ( step 1 ) .500 ( the OD ) minus .100 ( from step 1) = .400 drill size . Since the pitch is 10 or greater add .005" so the drill size is .405"eg. 3/4-6
1/6= .167" .750 - .167 = .583" ( 100% ) .167 X .05 = .008" ( to obtain 5% ) .583 + .008 = .591" ( 95%)thanks to Mack from Widell
Nominal Size (inches) |
T P I | Major Diameter (inches) |
Tapping Drill Size | Tapping Drill Size |
---|---|---|---|---|
BSP |
BSPT |
|||
1/16 |
28 |
0.304 |
6.6 mm | |
Letter drill G | ||||
1/8 |
28 |
0.383 |
8.8 mm | 8.4mm |
11/32 inch | 21/64" | |||
1/4 |
19 |
0.518 |
11.8 mm | 11.2mm |
29/64" |
7/16" | |||
3/8 |
19 |
0.656 |
15.25 mm | 14.75mm |
19/32" | 37/64" | |||
1/2 |
14 |
0.825 |
19.00mm | 18.25mm |
3/4" |
23/32" | |||
5/8 |
14 |
0.902 |
21 mm | |
53/64" | ||||
3/4 |
14 |
1.041 |
24.5 mm | 23.75mm |
31/32" | 15/16" | |||
7/8 |
14 |
1.189 |
28.25 mm | |
1-7/64" | ||||
1 inch |
11 |
1.309 |
30.75 mm | 30mm |
1-13/64" | 1-11/64" | |||
1-1/4" |
11 |
1.650 |
39.50 mm |
38.5mm |
1-35/64" | 1-33/64" | |||
1-1/2" |
11 |
1.882 |
45.5 mm |
44.5mm |
1-25/32" | 1-3/4" | |||
1-3/4" |
11 |
2.116 |
51.00 mm |
|
2" | ||||
2" |
11 |
2.347 |
57 mm |
56mm |
2-1/4" | 2-3/16" |
Trademarks are the properties of their respective owner(s).
The descriptions, illustrations, specifications, dimensions, and part numbers are subject to change without notice.
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