Fits perfectly in my Marineland C-360 canister filter. Only use the Marineland coarse filters though, I add different filter media and thickness sheets which I cut to size to achieve excellent water quality and for good measure, add Aqueon Bio-Balls in the top tray.
The whole wasn't deep enough and it didn't really fit
I got a small size one and it looked just like the one I got that was a different brand but the whole wasn't deep enough and I don't know about getting the medium one because it's too big.