INCH TAP DRILL SIZES

Recommended tap drill sizes (for approx. 75% thread)
INCH SIZES - NATIONAL COARSE   INCH SIZES - NATIONAL FINE
TAP SIZE DRILL SIZE   TAP SIZE DRILL SIZE
#1-64 #53   #0-80 3/64"
#2-56 #51   #1-72 #53
#3-48 5/64"   #2-64 #50
#4-40 #43   #3-56 #46
#5-40 #39   #4-48 #42
#6-32 #36   #5-44 #37
#8-32 #29   #6-40 #33
#10-24 #25   #8-36 #29
#12-24 #17   #10-32 #21
1/4-20 #7   #12-28 #15
5/16-18 F   1/4-28 #3
3/8-16 5/16   5/16-24 I
7/16-14 U   3/8-24 Q
1/2-13 27/64   7/16-20 W
9/16-12 31/64   1/2-20 29/64
5/8-11 17/32   9/16-18 33/64
3/4-10 21/32   5/8-18 37/64
7/8-9 49/64   3/4-16 11/16
1"-8 7/8   7/8-14 13/16
1-1/8-7 63/64   1"-14 15/16
1-1/4-7 1-7/64   1-1/8-12 1-3/64
1-1/2-6 1-11/32   1-1/4-12 1-11/64
1-3/4-5 1-35/64   1-1/2-12 1-27/64
2"-4-1/2 1-25/32   1-3/4-12 1-43/64
  2"-12 1-59/64
         
         
TAPER PIPE SIZES - NPT   STRAIGHT PIPE SIZES
TAP SIZE DRILL SIZE   TAP SIZE DRILL SIZE
1/8-27 R   1/8-27 S
1/4-18 7/16   1/4-18 29/64
3/8-18 37/64   3/8-18 19/32
1/2-14 23/32   1/2-14 47/64
3/4-14 59/64   3/4-14 15/16
1"-11-1/2 1-5/32   1"-11-1/2 1-3/16
1-1/4-11-1/2 1-1/2   1-1/4-11-1/2 1-33/64
1-1/2-11-1/2 1-47/64   1-1/2-11-1/2 1-3/4
2"-11-1/2 2-7/32   2"-11-1/2 2-7/32
2-1/2-8 2-5/8   2-1/2-8 2-21/32
3"-8 3-1/4   3"-8 3-9/32
3-1/2-8 3-3/4   3-1/2-8 3-25/32
4"-8 4-1/4   4"-8 4-9/32

METRIC TAP DRILL SIZES

Recommended tap drill sizes (for approx. 75% thread) 
     
METRIC COARSE SIZES       METRIC FINE SIZES
TAP SIZE DRILL SIZE       TAP SIZE DRILL SIZE
1mm x .25 .75mm       4 mm x .35 3.6mm
1.1 x .25 .85       4 x .5 3.5
1.2 x .25 .95       5 x .5 4.5
1.4 x .3 1.1       6 x .5 5.5
1.6 x .35 1.25       6 x .75 5.25
1.7 x .35 1.3       7 x .75 6.25
1.8 x .35 1.45       8 x .5 7.5
2 x .4 1.6       8 x .75 7.25
2.2 x .45 1.75       8 x 1 7
2.5 x .45 2.05       9 x 1 8
3 x .5 2.5       10 x .75 9.25
3.5 x .6 2.9       10 x 1 9
4 x .7 3.3       10 x 1.25 8.8
4.5 x .75 3.7       11 x 1 10
5 x .8 4.2       12 x .75 11.25
6 x 1 5       12 x 1 11
7 x 1 6       12 x 1.5 10.5
8 x 1.25 6.8       14 x 1 13
9 x 1.25 7.8       14 x 1.25 12.8
10 x 1.5 8.5       14 x 1.5 12.5
11 x 1.5 9.5       16 x 1 15
12 x 1.75 10.2       16 x 1.5 14.5
14 x 2 12       18 x 1 17
16 x 2 14       18 x 2 16
18 x 2.5 15.5       20 x 1 19
20 x 2.5 17.5       20 x 1.5 18.5
22 x 2.5 19.5       20 x 2 18
24 x 3 21       22 x 1 21
27 x 3 24       22 x 1.5 20.5
30 x 3.5 26.5       22 x 2 20
33 x 3.5 29.5       24 x 1.5 22.5
36 x 4 32       24 x 2 22
39 x 4 35       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