I have a Brompton and got some replacement 16" tubes from the LBS here in Japan but they only had tubes with Presta valves. The Brompton rims are Schraeder. Will the Presta tubes work OK on that oversized hole? I know the tube is inflated but I was wondering whether it would increase intrusion of water or maybe tube puncture at the valve.
Modern Schwalbe presta tubes come with something very similar to these. Something that screws onto the valve stem but is also an adapter. Your LBS will surely have some lying around that they can give you FOC if they use a lot of Schwalbe tubes.
dont worry about it...most presta valve tubes bring a little nut that helps the valve stay in place, but im not sure this is all that needed, once you put pressure in the tire and tube it wont move...in my humble opinion.