The Scrotal Shield for PosTVac Penis Pumps prevents your testicles from being pulled into the pump cylinder when pumping. The Scrotal Shield also helps create an air-tight seal if your public hair is untrimmed or you do not have Timm Medical Sealing and Lubricating Gel to use with your pump. You should choose the size that most closely matches the diameter of your erect penis. Once you achieve an erection and the tension ring is in place, remove the Scrotal Shield to proceed with sexual activity.