1.Material: made of durable nylon plastic, improves the durability and stability of the fin and plays an essential role when it comes to increasing stability, balancing steering manoeuvres and traction 2.Compatible size: the size of the surfboard fin is 18.4 x 3.5 x 21.5 cm, works on most SUPs or surfboards with a standard fin box, durable and stable to ensure your when surfing 3.Design: Our surfboard fin has a unique shape, the upper end is shaped like a fin and the streamlined appearance corresponds to the physical principles of water sports, which effectively improves the flexibility of the surfboard and improves its turning performance ly paddling 4.Easy to use: our fin for Sup has a lockable reinforcement buckle. You can first stick the fin base to the rear end of the surfboard, so you can install the SUP fin on the water ski base. If you no longer need the SUP fin in the future, slide the SUP fin buckle to remove it