The spline of the NRS Oar Right fits between the horns of an open oarlock to lock your oar blade in position for the most effective stroke. You can still feather the oar blade by simply tugging the oar in so the spline of the Oar Right clears the oarlock horns. For Carlisle and Cataract oars, use the Molded Oar Sleeve with the Oar Right for proper fit. Take care to read the instructions carefully. Only insert the screw into a wooden oar, this will damage Carlisle or Cataract oars. Small oar rights adjusts from 1 3/8 in. to 15/8 in. (Bluewater Oars and Economy Oars using XS Oar Sleeve). Sold individually.