Vac-U-Lock Knuckle UpTaking hands on play to the next level this feisty Knuckle Up accessory will delight and amaze you with this novelty functionality and its undeniable 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.