We offer three (3) different Fin Screw lengths based on the design conditions related to the installation and potential repair of a boat's Fin Box. Older wooden finboxes could have resin backfill from installation that limits the number of available threads, requiring a shorter screw. Current black finboxes use full 1" screws. If you are unsure which length to use, please contact us for help. Warning: Use of the incorrect length could lead to damage to your boat.