The shell. They're not flanged. Where it's pressed into the 510 connection, it's larger in diameter which prevents it from going all the way in to any of my tanks. Wouldn't be much of a problem except that because the bell bottom stops the carto from going all the way in, the punched holes don't quite reach the juice. Once I got it to fit, it works great just like the ones I've been peeling and slotting. The originals are exactly the same size. Where the problem comes in is I can slot them a bit higher than where the holes are punched.