|This feisty accessory will delight and amaze you with its novelty, functionality, and its undeniable ‘cool factor’. The "Knuckle-Up" is compatible with the entire selection of attachments, with its one-size-fits-all knuckle rings sitting below a standard Vac-U-Lock plug. You won’t believe how versatile this toy is! It’s 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.