"I know that these are meant to be flanges themselves, but I put my size 21 flanges inside my 28mm spectra cups and now that is the ONLY setup I use, it empties me better than anything else. I got an extra set of 21s because someone mentioned cutting them down a bit so they don’t stick out but I actually just like them better sticking out because it provides extra pressure. The suction is STRONG!" Spectra cups can be found here: https://www.spectrababyusa.com/shop/caracups/