The original A10 plunger cap nuts were chrome plated on my 1951 machine.
Suggest you purchase stainless steel replacements, and solve the inevitable corrosion issues that chrome plated nut will end up with.
Usually cheaper than re-plating.
Try Barleycorn Engineering.
Have a happy day, the BSA way.
Richard
PS; always put coppercoat (or equivalent) on SS threads, to prevent galling.