Bought this to replace an anatomical sleeve that came with a pump. The included sleeve was very soft and slipped into the pump causing a loss of vacuum, not ideal. This is vastly better, fits tightly around the pump base. It's gloriously smooth and with a bit of lube allows your to slide into the pump deliciously. Stays in place regardless of the pressure you increase in the pump, having tried it with the hand pump and motorised. This is a required purchase for an air tight seal and best result from your pump!