There was a rubber grommet that may be exactly the grommet that you mentioned that was available at my favorite bike shops for about a buck or buck fifty a pair, or you could go to a hardware store / electrical parts store and buy them for about $.05 each. The inside diameter of the hole was the size of a presta, and it was slotted around its rim to fit a bit larger hole (shraeder?) in sheet metal to protect what went through it. Its invisible if you use it on the inner side of a box section hollow rim, but still does a good job on a single walled rim. I've got that conversion on a mountain bike, and have been considering doing it to my wife's bike so that I don't have to switch the head on my frame pump when she has a flat. Of course she refuses to learn how to repair a flat, she just wants to have her mechanic along when it happens. Before that I used to cut a piece of inner tube and run the presta valve through a hole in that to protect the tube from the sharp edges of the valve hole, but I've gotten more than one flat doing that.
>>> HM & SS Sachs <firstname.lastname@example.org> 08/16/2004 9:28:34 PM >>>
Till this summer, I had routinely just ridden with presta tubes in Schraeder-valve rims, w/o problems. This summer I broke down and bought a new pump head (Silca), which actually grips the valve, and pulled out two valves while removing the pump head. For us bottom-feeders, this is almost major, and we certainly aren't going to
either use Schraeders or abandon the rims. I have found that some RadioShack rubber grommets designed to keep wires from fraying their insulation when they pass through metal chassis work fine as adapters.
Little tight setting, but some "303" rubber protector from REI did fine
to lube the rubber - and the tube for first insertion. This is hardly original with me, but I'll call it "research" instead of "plagiarism" since I've taken ideas from lots of people instead of just one... Maybe it will help you. Maybe you have found a better way; love to hear about it.