I bought the glass bottles based on the website saying they fit most pumps. I have the spectra s1, one of the most commonly purchased pumps on the market. The glass bottles do not fit the pump flange. DO NOT BUY if you are wanting to use with spectra. Sadly they don’t advise this on their website. Sadly they wouldn’t provide a reply paid return either saying it was my fault for buying them without double checking. Customer service was not helpful. If they had provided a reply paid option they would have had a customer who continued to buy from them many things for many years. However the overall experience was poor and I won’t be shopping with cherub again.