Apologies for the awful pictures (my camera's been..... no actually, there's no excuse for them) and the lack of any information at all about this:
I've just pulled an alu frame from the back of the shed, I think
it's around 10 years old, I've had it 4 or 5 years. It was bare, unfinished metal when I got it, but I made a half-assed, abortive attempt at painting it
which I shall be removing again shortly.
There's nothing stamped on it other than the frame number (AC912CO301) and 'B05' on the dropout. I've never had a mech hanger for it.
Any clues at all?