BS 4168-1 Hexagon Socket Head Cap Screws

BS 4168-1 specifies metric hexagon socket head cap screws. BSI lists ISO 4762 as the technically equivalent International Standard.

Technical line drawing of a hexagon socket head cap screw with length, thread diameter, head diameter, head height and socket references.

Selected metric dimensions — ISO 4762 reference

Thread d	Plain-head diameter dk min–max (mm)	Head height k min–max (mm)	Socket s (mm)	Socket depth t min (mm)
M3	5.32–5.50	2.86–3.00	2.5	1.3
M4	6.78–7.00	3.82–4.00	3	2.0
M5	8.28–8.50	4.82–5.00	4	2.5
M6	9.78–10.00	5.82–6.00	5	3.0
M8	12.73–13.00	7.64–8.00	6	4.0

Reference note: Selected plain-head values are in millimetres from the project ISO 4762 reference schedule. BSI lists ISO 4762 as technically equivalent to BS 4168-1. This is a short reference extract, not the full tolerance schedule; confirm the specified BS edition, property class and length before manufacture.