Most prewar British motorcycles used 1" (25,4mm) diameter handlebars. All Vincents have these and many Nortons pre 1955.
Triumph used their own system: 1" on the left and 15/16" on the twist grip side. Around 1960 this changed to 7/8" like everybody else.
At the moment I am moving the shop to a new location. I'll be in the shop on thursday and friday only.
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