All the Pro Series Mechanicals are compound approved for any set-up. They feature the New PRO TIP and “Snap Cup” design which holds all components in place for easy installation on your arrows. Super strong, razor sharp .035 stainless blades. No O rings , bands, or clips. Blades stay closed out of the fastest bows yet open smoothly on impact. CARNI-FOUR 4-BLADE - 4-blade, 1 ½” x 1 ¼” mechanical with Staggered Blade Technology that will change the mechanical world forever! The instant the two longer 1 ½” cut blades make contact and compress the internal spring, the two shorter 1 ¼” cut blades release and open with the touch of a hair! Giving you the largest 4-blade entrance hole on the market and an incredible “square” wound channel from start to finish!