TH Suitable for most of the Fins. Used to lock the fin after we insert it into the base to stop it from falling off. Removable and adjustable: The removable and adjustable design is easy to install and use and can meet your different requirements. Increase the stability and direction of the surf bar. Professional installation is highly recommended. A nice helper for you boat. This is a boat tail rudder which is made from high quality nylon materials with good toughness, high strength, low weight, high impact resistance, high heat resistance. Colour: Black Size: 1.4*4.1cm Delivery Quantity: 4 Pieces