saruSURF 4.6" US box center fin Safety Flex Soft replacement for longboard SUP Stand up Paddleboard River Surf Whitewater airSUP AIR7 Skeg with optional 'No-Tool' Fin Screw SAFETY FLEX SOFT 4.6" FIN - under most conditions this gummy fin is impossible to break , 12 month warranty , we call the fin "findestructible" ! FOR LONGBOARD , SUP AND INFLATABLE SUP ( inflatable sup boards with AIR7 fin box or US box - contact us to confirm if not sure) suitable for use with most longboard / (stand up paddle) SUP / airSUP. most long board and stand up paddleboards use the universal fin system, which can take this replacement fin. GREAT FOR SURFER AND ADVANCED SUP : surf dumping shore breaks, shallow reefs. On your SUP : challenge white water, low level streams, river runs and fly fish in shallow lakes. This fin is flexible , in most conditions will not break, and less likely to break out your board's fin box! GREAT FOR BEGINNER AND KIDS : 1st time surfing can be dangerous, usually the fin is the sharpest part of you board, with this fin you can feel safer - the fin will bend and flex more and is harder to hurt yourself and others STAINLESS STEEL FIN SCREW (optional) saruSURF brand US box center fin screw, no need to screw drivers, adjust your in position (forward, backward, take it off) anytime even out on the water! please choose if you need it, or if you have one already save some money!