Sperry A-2 series on the B-17, A-13 series on the B-24.
Both are identical from the top of the hangar cradle downwards, the only difference being the support rod; fixed on the B-17, hydraulically retractable on the B-24.
The AAF manual for these is AN 11-45G-1 Handbook of Instructions for Lower Ball Turrets Types A-2, A-2A, and A-13, I've not found the number for the parts catalog as yet.
Sperry A-2 series on the B-17, A-13 series on the B-24.
The AAF manual for these is AN 11-45G-1 Handbook of Instructions for Lower Ball Turrets Types A-2, A-2A, and A-13
Whilst you're waiting for a reply Roman, is this pic any use? Taken at Duxford, the turret removed from 'Mary Alice', as she undergoes deep maintenance.