Billy Mate 18-14mm Diffused Downstem 13cmBilly Mate 18 14mm Diffused Downstems 13cm These quality diffused downstems are made with strong but thin 2mm glass by Billy Mate. Your downstem is the only part of your bong where you actually want thinner glass, so the bottom opening is wider meaning it won't clog as often. Comes in blue green or black. 13cm in length please see photos for correct measurement. 18 19mm male joint 14mm female joints 13cm Diffuser downstem