I bought size 10 corks to put in a 2 liter soda bottle that fits an animal water fountain that I bought for our cats and dog. The water came out of the bottle itself to fast. We drilled a small hole in the center of the cork then put it in the bottle and then screwed the 2 liter bottle in the water fountain. It works perfect. I felt like an absolute genius. So happy with my corks. They shipped from Texas and I received them in Virginia in 3 days. I couldn't believe I got them that fast. Nothing but excellent service. I can't say enough good things about WidgetCo. I don't know a thing about mm but we found a conversion chart from inches to mm and was able to figure out what size we needed. So happy. Thank you WidgetCo.