Originally Posted by
JohnDThompson
And that's one of the reasons the stems come with those little knurled nuts that people generally discard.
As Looigi noted, not all Presta stems are threaded and those nuts serve only that limited purpose. I discard them because the are a nuisance when you do have to repair a flat, both to remove the tire/tube and to reinstall it. Pressing with my thumb is easier.