fietsbob

I Note There is an Unthreaded portion of presta stems, that is where the air seal gasket grips.

its between the smaller coarse thread on the end, and the larger finer thread for the ring nut.

then You can pull the air chuck off. with little effort.

If you shove it up on the fine threaded part of the stem,
you are just making work for yourself that is counterproductive.

as is a screw on pump head on a removable valve stem ,
as unscrewing one will unscrew the other, a push on/ pull off pump head
is so much more sensible..