Only the ‘works’ TT clutches had a plain “machined from the solid” pressure plate. Production road bikes have the pressed and dished plate. I’m not sure when the three adjustable thrust pins replaced the earlier, non-adjustable 3/8″ diameter solid thrust pins, probably early to mid 1930s. The nuts are 5/16″ Cycle thread, but 1/4″ spanner size, which is 0.445″ across the flats.
