BS 7419 Holding-Down Bolts

BS 7419 specifies holding-down bolts for connecting steel structures to foundations. It includes square-head bolts and hexagon-head bolts, thread sizes M16 to M64, product grade C.

Dimensioned line drawing of a holding-down bolt with hexagon and square head options, labelled thread d, length l, head height k and across-flats dimensions.

Selected BS 7419 hexagon-head dimensions

Thread d	Pitch P (mm)	Shank ds min–max (mm)	Hex width s min–max (mm)	Head height k min–max (mm)
M16	2.0	15.3–16.7	23.16–24.00	9.25–10.75
M20	2.5	19.16–20.84	29.16–30.00	11.60–13.40
M24	3.0	23.16–24.84	35.00–36.00	14.10–15.90
M30	3.5	29.16–30.84	45.00–46.00	17.65–19.75
M36	4.0	35.00–37.00	53.80–55.00	21.45–23.55

Thread d	Thread length b min–max (mm)
M16	116–122
M20	120–127.5
M24	124–133
M30	130–140.5
M36	136–148

Reference note: Selected dimensions in millimetres for the hexagon-head form, M16–M36. The standard also covers square-head forms and sizes up to M64; use the relevant full table for the chosen head form and size.