There are six categories of standard taps. We have broken down the drill size recommendations into those six categories which appear below
Metric Size
Letter Size
Metric taps
milimeter Thread
Tap Size
Drill Size
M1.6 x 0.35
1.25mm
M2 x 0.4
1/16
M2.5 x 0.45
2.05mm
M3 x 0.5
#40
M3 x 0.6
2.5mm
M3.5 x 0.6
#33
M4 x 0.7
3.3mm
M4 x 0.75
3.4mm
M5 x 0.8
4.2mm
M5 x 0.9
M6 x 1
5mm
M6.3 x 1
5.5mm
M7 x 1
6.1mm
M8 x 1
7.1mm
M8 x 1.25
6.7mm
M9 x 0.75
8.3mm
M9 x 1
8.1mm
M9 x 1.25
7.9mm
M10 x 1
9.1mm
M10 x 1.25
8.9mm
M10 x 1.5
8.4mm
M11 x 1.50
9.7mm
M12 x 1.25
10.9mm
M12 x 1.5
10.7mm
M12 x 1.75
13/32
M14 x 1.25
12.8mm
M14 x 1.5
12.7mm
M14 x 2
15/32
M16 x 1.5
14.7mm
M16 x 2
35/64
M18 x 1.5
16.8mm
M18 x 2.5
15.8mm
M20 x 2.5
11/16
M22 x 1.5
20.9mm
M24 x 2
22.3mm
M24 x 3
53/64
M30 x 3.5
1-3/64
M36 x 4
1-1/4
NC taps
National Coars
1/4-20NC
#8
5/16-18NC
F
3/8-16NC
5/16
7/16-14NC
U
1/2-13NC
27/64
9/16-12NC
31/64
5/8-11NC
14mm
3/4-10NC
21/32
7/8-9NC
49/64
1-8NC
7/8
1 1/8-7NC
63/64
1 1/4-7NC
1-7/64
1 3/8-6NC
1-3/16
1 1/2-6NC
1-11/32
NS taps
National Standard
5/32-32NS
1/8
5/32-36NS
#30
3/16-24NS
#26
3/16-32NS
#22
7/32-24NS
#16
7/32-32NS
#12
1/4-32NS
7/32
1/4-40NS
#1
5/16-32NS
9/32
11/16-16NS
5/8
1-14NS
15/16
NPT taps
National Pipe Thread
1/8-27NPT
R
1/4-18NPT
7/16
3/8-18NPT
15mm
1/2-14NPT
23/32
3/4-14NPT
59/64
1 x11-1/2NPT
1-5/32
1-1/4x11-1/2NPT
1-1/2
1-1/2x11-1/2NPT
1-47/64
2x 11-1/2NPT
2-7/32
NF taps
National Fine
1/4-28NF
#3
5/16-24NF
I
3/8-24NF
Q
7/16-20NF
W
1/2-20NF
29/64
9/16-18NF
33/64
5/8-18NF
37/64
3/4-16NF
7/8-14NF
13/16
1-12NF
29/32
1 1/8-12NF
1 1/4-12NF
1-11/64
1 3/8-12NF
1-19/64
1 1/2-12NF
1-27/64
Number Size Taps
Number size Thread
0-80
3/64
1-64
#53
1-72
2-56
#51
2-64
#50
3-48
5/64
3-56
#46
4-36
#44
4-40
4-48
#42
5-40
#39
5-44
#38
6-32
#36
6-40
8-32
#29
8-36
10-24
#25
10-32
#21
12-24
#17
12-28
#15
14-20
#10
14-24
#7