Thread Comparisons - Bolts and machine screws

Metric

 

Imperial - threads per inch

ISO metric

TPI

Pitch (mm)

 

 Inch dia

UNC

Whit.

UNF

M3 (0.118”)

51

0.5

 

-

-

-

M4 (0.158”)

36.3

0.7

 

-

-

-

M5 (0.197”)

31.8

0.8

 

 3/16”(0.187)

24

24

-

M6 (0.236”)

25.4

1.0

 

 1/4”(0.250)

20

20

28

M8 (0.315”)

20.3

1.25

 

 5/16”(0.312)

18

18

24

M10 (0.394”)

16.9

1.5

 

 3/8”(0.375)

16

16

24

M12 (0.472”)

14.5

1.75

 

 1/2”(0.500)

13

12

20

M16 (0.630”)

12.7

2.0

 

 5/8”(0.625)

11

11

18

NB. UNC and Whitworth are for most purposes interchangeable except for ½", where UNC has a finer pitch.

Nomenclature is as follows:

Coach Bolt - Cup Square bolt - partially threaded

CSMS - countersunk machine screw - threaded right up to the head

Hex Set - Hex headed machine screw - threaded right up to the head

RHMS - Round head machine screw - threaded right up to the head