A device comprising a substantially vertical post member that can be adjusted longitudinally within a fin box and remain vertical, riding adjustably in a longitudinally oriented slot and thereby protrudes from the bottom of a standard fin box customarily installed in personal watercraft such as a surfboard, sailboard, paddleboard, and the like. The securable end of a removable fin is dropped over the post and held in place by a nut, clip, hook, or clamp.