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Metric Bolt Head and Wrench Size

ANSI/SO, DIN and JIS bolts.

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ANSI/ISO, DIN and JIS metric bolt head and wrench sizes:

ISO Metric Threaded Bolt
Spanner or Wrench Size (mm) Allen Key
3 5.5
4 7 7 7
5 8 8 8 4
6 10 10 10 5
7   11  
8 13 13 12 6
10 15, 16 17 14 8
12 18 19 17 10
14 21 22 19
16 24 24 22 14
18   27  
20 30 30   17
24 36 19
  • ANSI B18.2.3.9M Metric Heavy Hex Flange Screws
  • ISO 4228 Spanners and wrenches -- Spline drive ends for power socket wrenches
  • ISO 724 - Metric Threads

An Allen key, Allen wrench or hex key is a tool used to drive bolts and screws with hexagonal sockets in their heads.

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