air7 Stainless Steel 316 fin screw [ 2 pack] for Longboard Surfboard, Stand Up Paddle (SUP) and airSUP - most US box fin boxes air7 stainless steel fin screws for most SUP including inflatable airSUP bolt : 3.5mm Diameter x 18mmLength nut : 14.1mm Wide x 14.1mm Length x 4mm Height note: two in the pack fits most US box style fin boxes (longboard / SUP and airSUP)