Taking hands-on play to the next level, this feisty Knuckle Up accessory will delight and amaze you with its novelty, functionality, and its undeniable cool factor. The Knuckle Up accessory is compatible with the entire selection of Vac U Lock attachments, with its one size fits all knuckle rings sitting below a standard Vac U Lock plug. You wont believe how versatile this toy is! Its perfect for both masturbation and playing with a partner! What are you waiting for?! Experience endless pleasurable possibilities with the most user friendly sex toy system in the world.