A single row corn harvesting unit of a normally multiple unit corn head adapted to be mounted at the forward end of a crop harvesting combine and comprising a pair of "snapping rolls" or stalk rolls extending forwardly in cantilever fashion in contiguous relation to each other from a gear subassembly, the snapping rolls cooperating with each other in the corn harvesting operation. The rearward end of each snapping roll has a driven bevel gear mounted thereon, the two driven bevel gears comprising part of the gear subassembly. A drive shaft is suitably mounted for rotation and a double bevel gear which also forms part of the gear subassembly is mounted on the drive shaft. The double bevel gear has opposed gear faces each respectively adapted to drivingly engage a corresponding driven bevel gear on one of said respective snapping rolls. The double bevel gear has a spline on the inner periphery thereof and the portion of the axial length of the drive shaft which receives the double bevel gear has a spline on the outer periphery thereof which is adapted to receive and to mate with the spline on the inner periphery of the double bevel gear, whereby the double bevel gear is freely slidable along the spline on the drive shaft to permit the double bevel gear to automatically center itself with respect to the driven bevel gears on the snapping rolls.