Originally Posted by Riveting

This is said a lot. But the problem is that some pumps need to be secured by pushing the pump down onto the stem with one hand, while the other hand has to flip the lever 90° to secure/squeeze the pump nozzle to the stem. I personally don't have a third hand to push down on the opposite side of the tire to stop the stem from going into the rim, therefore I use the the little round nut to hold the stem in place.