BS 4168-9 Hexagon Socket Wrench Keys

BS 4168-9 specifies metric wrench keys used with the hexagon socket screws in Parts 1 to 8. Its successor, BS ISO 2936, covers hexagon socket screw keys.

Technical line drawing of an L-shaped hexagon socket wrench key with long-arm length, short-arm length and across-flats size references.

Selected wrench-key dimensions — ISO 2936 successor reference

Key size s (mm)	Long arm L1 (mm)	Short arm L2 (mm)
2	50	16
3	63	20
4	70	25
5	80	28
6	90	32

Reference note: Selected values in millimetres are from the project ISO 2936 schedule, the successor that replaced BS 4168-9. This is a short reference extract; confirm key tolerances, material, hardness and performance requirements against the applicable edition.