Abstract: The pinion gear of a gear pump is press fit onto the end portion of the drive shaft of the pump and is positively captivated on the shaft by a key and by a hot upsetting process, the latter resulting in the formation of axially protruding burrs on the end face of the shaft. When the drive shaft is rammed forwardly with significant force, the burrs tend to embed in an end plate disposed in opposing relation with the shaft. To prevent the burrs from embedding in the end plate and locking the shaft against rotation, the end plate is formed with a recess which receives the burrs with substantial axial clearance when the shaft is rammed forwardly against the end plate.