To use a push-type, hand-operated grease gun, you connect the nozzle of the gun to its corresponding fitting at the lubrication point and work the handle in and out. To connect the gun, align the nozzle and the fitting end-to-end and push on the gun handle so the nozzle slips over the hydraulic fitting or into the flush fitting. At the same time that the nozzle mates with the fitting, the handle moves inward to build pressure inside the gun to force grease out of the nozzle and into the fitting. Then, let up on the handle a moment. A spring in the gun will then force the handle out a little way and prepare the gun for another inward stroke of the handle.
When you connect the push-type gun to a hydraulic fitting, the nozzle grips the fitting and is held firmly only as long as the nozzle and fitting are aligned or until pulled free. In connecting the gun to a flush type fitting, however, you must keep a steady pressure on the fitting because the nozzle doesn't grip the fitting (fig 7-23B)