Block Surf California Twin Fin Set What's old is new! Hold an edge like never before. Allows dropknee and standup riders to put more torque into their bottom turns. You can even customize the size and shape of the skegs using a sharp knife (at your own risk). This set of two skegs/fins comes with 4 screws are for the bottom of your bodyboard are made of flexible, durable plastic. To install, you only need to punch four holes through your board and pop the screws through to connect with the skegs on the bottom Distance between screw holes on skeg: 4 inches Skeg length from front to back along the base: 5 inches Skeg height from base to tip: 3.5 inches Screw length: 2 inches Maximum board thickness these will work with: 2.75 inches