Pack of 10 rubber grommets for sealing downstem sleeve to water pipe. Comes in 5 sizes. 10 mil slip-in, 10mil donut, 12mil donut, 12mil top hat and 15mil top hat. THIS IS THE INSIDE DIAMETER OF THE GROMMET. Allow an extra 3mm to fit in hole. e.g. 12mm grommet on downstem will fit 15mm hole. Please choose size or choose random for a mixed pack. Mixed pack can be custom ordered in the comments section at checkout. High quality American made rubber seal. "10mil donut and 10mil slip in are good quality soft rubber and stretches over 12mil downstems with ease" Be sure to use a little soapy water. Please see Glass Accessories Measuring Guide.