313652 has one too.
Still fitting them the day after yours was built.
My March of 1974 Commando, #313641 has the nipple on the swing arm.
My 1974 Norton Commando 850 Roadster MK2 #313641 (Date "3 74" on plate). Very close to yours. 1974 models are arguably the best year of Commandos!
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