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No problem.
It has the usual third strap at the rear, for attachment to the head or seat tube, to stop it flapping around.
I couldn't find it on Carradice, but it is round in cross-section and measures 27cm wide, 16cm high and 13cm wide.
It's much smaller than the "proper" saddlebag: I used it for chucking a large D-lock, keys, phone etc in.
If memory serves, it holds four 500ml tins of beer exactly.
Apologies, I mean the bar/saddle bag, is that a bit smaller than the one that uses the support?
Or do you know which model name it is? Sorry to be awkward is for the gf @Scilly.Suffolk