Hi Mark.Thank you for drawing my attention to this part. Until you posted , I never knew it existed.I notice it's listed in the 1946 Parts catalouge but only for the C10 & C11 models. Was it fitted to pre war & wartime M series bikes?
I think that's a question for the experts Hamish,
Where I would have expected a swivel joint, I found mine fixed.
My friend's bike had been bending brake rods, so he adapted his to swivel.
Now I have saved him the embarrassment of not have the correct part fitted, well maybe.
BTW they should be on our stocklist in a day or so now.