Originally Posted by
JohnDThompson
And that's one of the reasons the stems come with those little knurled nuts that people generally discard.
The Michelin road tubes I used don't even have threaded stems, much less nuts. However, pushing inward on the deflated tire at the position of the stem will support it so that you can get the pump head on. Once mostly inflated, the air pressure supports the stem well enough to attach the air chuck.
At the low pressures with fat MTB tires, the nut is more useful.