Reducing Diffuser will allow you to transform your 18.8mm joint size bong to 14.5mm joint size. The male joint is 18.8mm, but the female joint is 14.5mm to take 14.5mm size bowls or accessorries . These borosilicate glass downstems will act as adapters when you have differring joint sizes between your accessoriies and bong . They have hand firecut diffuser pin holes for strength and hand ground joints for a snug fit and the EDIT Logo , Available in various lengths