This OVERSIZE glass downstem sleeve has an outside diameter of 15.5mil and inside diameter of 12.5mil. Different lengths available. Please choose length above. Measured from top to bottom. Handmade item so may be slight variation in size. OVERSIZE ITEM. With included top hat grommet this downstem fits into 18mm hole in your waterpipe. Can be used with 9mil, 10mil and 12mil sliders. 15.5mil is approx 5/8" 12.5mm is approx 1/2" OVERSIZE ITEM. Please be sure to order correct size. TIP:Use a little soapy water when sliding rubber grommet on to downstem. Please see Glass Accessories Measuring Guide.