Thanks to Klaus who solved my problem between a 1958>62 7" Full Cast rear hub and a 42 Tooth sprocket that would not fit the bolt holes. The sprocket, unmarked with a part, turns out to be for an Ariel Full Width Alloy 56>57 rear hub and bolt holes have a 5/16" wider spacing.
I can easily get an engineer in Kenya to turn 4 new bolt holes and countersinks in this sprocket, which must be partno 42-6069, that will match the BSA Full Width steel hub bolts.
But what about the rest, i.e. bearings and matching, spacers etc? Are the two hubs (Ariel Alloy and BSA Full Steel)compatible in width and sprocket mating? Any ideas welcome. SH spares are pure Unobtanium where I live in Africa.
Cheers