" 1/4"" Aluminum Hold Down Clamp & 1/4"" x 20 tpi Bolt & Knob Material:Aluminum Secure work piece easily to any T-track equiped jig. Each hold down includes sliding bolt, hold down and knob. These PVC Tipped Hold-Down Clamps feature non-marring PVC tips that are the perfect tool for working with softer woods, finished surfaces or for any stock that needs to kept in place. The PVC also gives you more gripping power when pressure is applied to your stock. This prevents slipping and walking of your wood especially when drilling on a drill press. Our PVC tipped hold downs come with a star knob and bolt and are available in the two most commonly used sizes of 1/4"" x 20 and 3/8 x 16. "