BS 1769

BS 1769 covers Unified black hexagon bolts, screws and nuts in the heavy series. The table shows selected bolt and screw head dimensions from the published schedule.

Line drawing of a heavy-series hexagon bolt with nominal size, shank diameter, head thickness, length and width across flats marked.

Selected hexagon head bolt and screw dimensions

Nominal size D (in.)	Threads per inch UNC / UNF	Across flats A max. (in.)	Across flats A min. (in.)	Across corners C max. (in.)	Head thickness F max. (in.)	Head thickness F min. (in.)
1/2	13 / 20	0.8750	0.8550	1.01	0.426	0.386
5/8	11 / 18	1.0625	1.0375	1.23	0.522	0.478
3/4	10 / 16	1.2500	1.2250	1.44	0.618	0.570
7/8	9 / 14	1.4375	1.4075	1.66	0.714	0.662

Note: Values are inches. These are selected rows for the heavy series; the standard also covers other diameters, lengths, nuts and finish conditions.