For sale is a used Boston Gear Reductor - flanged Reductor - Ratiomotor with a #60 nine tooth 3/4" chain sprocket.  This is used but turns freely.  Labeling indicates:  Type UAF, Size 17, Ratio 50, IP HP 1/6, IP RPM 1750, OP RPM 35.  Output shaft size is 3/4" and input shaft is 5/8".