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Spanner Tables

Spanners designed for use on BSW or BSF Hex products will be stamped with the thread diameter of the bolt that they fit, but this size stamp will not be the "across-flats" size of the nut or screw head. The following table lists the approximate across-flats measurement of BSW/BSF Hex products of different thread diameters.

Thread Diameter

Across Flats Size

1/4"

0.44"

5/16"

0.52"

3/8"

0.60"

7/16"

0.71"

1/2"

0.81"

5/8"

1.00"

3/4"

1.20"

 

The following table shows the size of Allen key required for Metric screws of various thread diameters. Please note that Socket Cap Screws require a slightly larger Allen key than Button Head, Countersunk or Flanged Sockets.

Thread Outside Diameter

Allen key for Socket Caps

Allen key for other head styles

  3 mm

2.5 mm

   2 mm

  4 mm

   3 mm

2.5 mm

  5 mm

   4 mm

   3 mm

  6 mm

   5 mm

   4 mm

  8 mm

   6 mm

   5 mm

10 mm

   8 mm

   6 mm

12 mm

10 mm

   

 

The following table lists the spanner sizes that fit Metric Hex products of different thread diameters.

Thread Diameter

Spanner Size

  3 mm

5.5 mm 

  4 mm

  7 mm

  5 mm

  8 mm

  6 mm

10 mm

  8 mm

13 mm

10 mm

17 mm

12 mm

19 mm

14 mm

22 mm

16 mm

24 mm

 

The following table lists the most common AF ("Across Flats") spanner sizes that fit UNC and UNF Hex products of different thread diameters.

Thread Diameter

Spanner Size

3/16"

5/16"

1/4"

7/16"

5/16"

1/2"

3/8"

9/16"

7/16"

11/16"

1/2"

3/4"

9/16"

7/8"

5/8"

1"

3/4"

1 1/8"