socket wrenches
metric sizes

The tables below show the commonly-available sizes of metric socket wrench and the fasteners they fit. A 12-pt socket fits both hexagonal, square, and 12-pt heads (the last found mainly in aerospace bolts, but also on automobile engines as, for example, head bolts).

Sockets are made that are deeper than the normal socket, so that they will fit over bolts that protrude so far that a normal socket will not come down far enough to engage the nut. In the column headings, these are indicated by a “d”.

One end of a socket has a square recess which fits the socket wrench. In consumer wrenches, the square drives are ¼″, 3/8″, ½″, and ¾″.

American Socket Wrenches: Metric Sizes to 36mm
Size
(mm)
¼″ drive 3/8″ drive ½″ drive Fits bolt or nut with this diameter
6
pt
12
pt
6pt
d
6
pt
12
pt
6pt
d
12pt
d
6
pt
12
pt
6pt
d
12
d
ANSI
cap screws,
formed hex screws,
standard metric
ANSI
heavy hex
ISO J.I.S.
(Japan)
D.I.N
(Germany)
3                                
4 .                     M2 × 0.4        
5 .                     M2.5 × 0.45        
5.5                       M3 × 0.5   3   3
6 .                     M3.5 × 0.6     3  
7 .                     M4 × 0.7   4   4
8 .                     M5 × 0.8     4 5
9 .     . . . . . .           5  
10 .     . . . . . .     M6 × 1     6 6
11 .     . . . . . .         7 7 7
12 . . . . . . . . .         8    
13 . . . . . . . . .     M8 × 1.25       8
14   .   . . . . . .   .     10 8  
15       . . . . . .     M10 × 1.5*        
16         . . .   .     M10 × 1.5        
17       . . . . . .   .     12 10 10
18         . . .   .     M12 × 1.75        
19       . . . . . .   .     14 12 12
20                                
21                 .   . M14 × 2 M12 × 1.75   14  
22               . .   .     16   14
23                             16  
24                 .     M16 × 2 M14 × 2     16
27                 .   .   M16 × 2      
30                 .     M20 × 2.5        
32                 .              
34                         M20 × 2.5      
36                 .     M24 × 3        

* Produced in the US, but not an ISO size. The 16mm between flats should be used instead.

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