COMPATIBLE WITH: iROCKER - BLACKFIN (NOT ULTRA(TM) BOARDS) Whether you&';re an experienced paddler or new to the sport, sometimes we all lose a fin. This replacement flip-lock center fin is compatible with 2020 and newer iROCKER and BLACKFIN models. 1 x 9" Please Note: Older boards 2021 and older may not be fully compatible with new replacement fins. If you need to make small adjustments to the length of your fin to achieve optimal fit, we recommend filing the edges of the fin with sandpaper.