The use of a penis pump creates a level of vacuum that will stretch and enlarge tissues. This high-expansion cylinder is cast of clear Lucite. It is flared outward at the bottom and has a slight inward roll at the opening, which acts as a built-in cockring and a comfortable seal without messy gaskets. This 9.5in long cylinder also features a state-of-the-art connector/air valve that allows the pump to be disconnected from the expansion cylinder while maintaining the exact pressure you choose. It also features a growth indicator to measure your progress. This 2.5 inch Boston Pump Works Lucite Cylinder fits basic Boston Pump Works Pump. Come grow with the Cadillac of pumps and pump accessories!