Threading on GB Sport brake calipers

[rogerzilla]

Any ideas what they might be? I want to replace a couple of the rusted dome nuts. An M6 nut threads onto the main spindle nicely but I suspect it's actually 0BA or something else non-metric. The cable clamp could be 2BA (easily confused for M5)? Or did they go metric by the 1960s?

 

[Hover Fly]

They were still thinking about metric in the early sixties, I doubt if GB would have re-tooled. Can you hold a known metric rod against the screw to compare thread angle (47.5/60 deg,) and round (BA) against metric flat thread crests? Theres no BSC that could be confused.