You will receive 10 food grade silicone rubber grommets. I have experimented with several of the rubber grommets available to make mason jar lids and these are by far the best! No more weird tastes from off gassing rubber. They fit the "Mainstays" brand of mason jar lid perfectly without the need for an o-ring. All you need is a 7/16" drill bit to make a hole in your lid. Once installed, the lid is leak proof. They are dishwasher safe as well. Save your spaghetti sauce jars and make your own reusable drink containers for a fraction of the cost! If you are installing them in a metal lid be very careful as they are soft and will cut fairly easily.