Tap Drill Sizes

link to Inch tables         link to Metric tables    

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

Acme |   BSP & BSPT |   Pg



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
----------------------------

 

PG Tap drill sizes

 

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

 



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:




tap drill size for acme taps.

this is for information only

link to Acme Tap page


tap drill size for acme taps

 

Based on a 100% of thread as per ANSI

to calculate tap drill size for acme taps.

 

the magic formula

step 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

 


BSP and BSPT

suggested tap drill sizes

British Standard Pipe
Parallel or Taper
BSP or BSPT

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"

 



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