Tap Drill Sizes

link to Inch tables         link to Metric tables    

link to Tap Drill size calculator (for inch size taps)



INCH TAP DRILL SIZES

 

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 		#39 
#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
----------------------------




METRIC TAP DRILL SIZES
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
----------------------------


Newman Tool's handy hint.

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.

 

Tap Drill Calculator for Inch Sizes

Cut Thead Only


Tap drill size size formula's are theoretical based on the thread type and desired percentage of thread. Please allow for the fact that drills generally drill oversize.


Enter appropriate values and press Calculate
( enter diameter in decimals eg .500 for 1/2",
"do not to use fractions"

use 75 if you're not sure about the percentage)

Tap Diameter (in decimal inches)

"do not to use fractions"

Threads per Inch

Percent of Thread
use 75 if you're not sure about the percentage



Drill Size:




link to Drill size for Acme tap page

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