Pump Couplings SAFETY WARNING ! U.S. Safety Standard precludes the use of P.T.O. adaptors that could extend the tractor P.T.O. shaft with the possibility of the universal joint protruding BEYOND THE TRACTOR SAFETY SHIELD. THESE COUPLINGS ARE DESIGNED TO FIT PUMPS WITH ROUND INPUT SHAFTS. ROUND BORE PUMP COUPLINGS PART No. SPLINE BORE ROUND BORE LENGTH B6691 1 3/8" 6 spline 5/8" bore 3 3/4" B2711 3/4" bore B2712 7/8" bore B2713 1" bore B2902 1 3/8" 21 spline 3/4" bore B2903 7/8" bore