And size of the sup fin screws: M4 x 16 mm, the square part: 13 mm x 13 mm x 3 mm. The SUP screw is the essential accessory for surfboard. Fin screw with silicone seal: Our SUP paddleboard screws are equipped with a black silicone seal for each fin screw, which can screw stainless steel suction screw and the surfboard more firmly and increase stability between the screw and the longboard.
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