Small: Attaches Directly To Medium: Directly Attaches To Large: Intended For If you are not using oar rights, plastic stoppers will position and keep your oars where you want them to be. Use large stoppers with Molded Oar Sleeves. Small: Mounts directly on small-diameter shafts 1 3/8" - 1 5/8". Regular: Mounts directly on Carlisle or Cataract shafts 1 7/8" - 2". Large: For larger-diameter shafts, Molded Oar Sleeves, or wraps 2" - 2 1/4"