Center Fin 5.5" For longboard SUP, airSUP For Stand Up Paddle Boards 5.5" black plastic keel fin 5.5" (145mm) (Accessories) Center fin x 1 , with "no tools" Stainless 316 fin screw (the nut and bolt) ==== Fin: H = 5.5" Base = 175mm x 9mm Pin = 14 x 4.5mm Fin Screw: Made of salt water resistant stainless steel. Screw part: 0.15 inch (3.8 mm) diameter x 0.71 inch (18 mm) length Nut part: 0.6 x 0.5 x 0.2 inches (14 x 14 x 4 No tools required fin screws