51 Series Motor Bi-Rotational Tandem Unit 2 Stages Sae 4 Bolt B Sec 7/8-13 Spline Shaft With OB Bearing First Stage 2-1/2 Gear Width Gear Housing Orb #20 Inlet Port Orb #20 Outlet Port Unported Bearing Carrier Second Stage 1 Gear Width Gear Housing Port End Cover Orb #12 Rear Inlet Port Orb #12 Rear Outlet Port Extended Studs Top