I couldn't find 21mm flanges anywhere and the slightly larger ones I had were excruciating to use. Just when I had given up, I ran across these Mama & Roo's flanges.
The flanges shipped within hours of my order being placed and arrived in just a couple of days. The sizing was perfect and I am no longer in pain when I pump. Most definitely worth every cent!!
21mm flange for Spectra pumps, wide mouth bottle connector, valve, membrane