I recently mounted a pair of metal stem tubes in my newly restored 23¨ Hayes TT wheels and ran into an interference problem with the valve stem cover not sliding down far enough to engage the rim nut threads.
You can see that the valve cover is tall enough to do the job, but the valve stem transition from wide to narrow diameter is so far up the stem that it interferes with the fluting in the cover. The result is that the cover is prevented from slipping down far enough to screw on.
What to do ?
I could: (1) Add some washers or a spacer of some kind below the rim nut to raise it; (2) Try and find fatter valve stem covers or ones w/o the fluting that would successfully slide over the valve stem; or (3) ask the forum members for their suggestions.
Rich, there are multiple lengths and shapes to that style of valve cover. Longer ones may fit. There are others which neck down just at the thread, leaving the barrel of the cover larger.
If you can't find similar looking ones, a set of Dill easy-on type would do the trick. These have a sliding threaded piece inside which allows you to fit them to various length stems. The thread engagement is on the small end where a modern valve cap would be screwed.
Somewhere I have a spare set of Dills in an original box, but I haven't seen them for a while.
Allan from down under.