Complex sentence: A testicle cuff is a ring-shaped device to restrain a testicle within the scrotum (i.e., when closed it does not allow the testicle to pass through it); they come in pairs and are one of many different gadgets for restraining the male genitalia.
Split into simpler sentences: A testicle cuff is a ring-shaped device around the scrotum between the body and the testicles such that when closed it does not allow the testicles to pass through it. They are one of many different gadgets for restraining the male genitalia.