INCH TAP DRILL SIZES
Recommended tap drill sizes (for approx. 75% thread)

INCH SIZES 

NATIONAL COARSE

INCH SIZES

NATIONAL FINE

TAP            DRILL
SIZE           SIZE
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
#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

STRAIGHT PIPE SIZES

NPS

TAP            DRILL
SIZE           SIZE
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
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 METRIC FINE SIZES
TAP              DRILL
SIZE             SIZE
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
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
8 x .75          7.25
8 x 1            7.5
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

Notes: Tap Drill Sizes (inch) for a 75% Thread
In general, you can find the tap-drill for any size 60 degree thread, subtract one pitch length from the major diameter.

Formula: Major Dia. minus One Pitch Length equals tap-drill size

English Example for 3/8-16 thread: .375 - .0625 = .3125 tap-drill (5/16)

Metric Example for M6 X 1 thread: 6mm - 1mm = 5mm tap-drill

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