Downstems come in a variety of different downstem sizes. To find the right fit, you need to know what size your waterpipe takes. First you need to know what length you need. A downstem should come to the bottom of the water pipe but not touch. You will need to measure with a ruler if you have a current downstem that needs to be replaced, or try and hold the ruler to the base of the water pipe if possible. White Rhino downstem sizes range from 3 inches up to 6 inches. Next, you will need to know if the water pipe joint is 14mm or 19mm. The White Rhino glass downstems are 19/14, meaning the outer diameter is 19mm, and the inner hole is 14mm for a 14mm bowl or banger.