Carbon Express BullDog Nock Collars X-Buster 600 12 Pieces Silver. Helps prevent cracks from nock end impacts. Specifications for Carbon Express BullDog Nock Collars: Manufacturer: Carbon Express Color: Silver Quantity: 12 Features of Carbon Express Nock Collars: Provides protection from nock end impacts Helps prevent cracks from nock end impacts Available in sizes: Tank 23D 350/X-Buster (400) Tank 23D 400/X-Buster (500) Tank 27 Tank 25 X-Buster (350 600 700) Package Contents: Carbon Express BullDog Nock Collars Carbon Express 50253: BullDog Nock Collars X-Buster 600 12 Pieces Silver