Genuine Innovations Presta Valve Adapter
Enable a Presta valve to be mated with a Schrader valve bike pump.
Does what is is supposed do. Put one in your bag... now!
I bought one and threw it in my seat bag. Easy to use and gives you more options when you're low on air.
Works great, order two and leave em on your bike. If your pump breaks, like mine did, you can fill up at a gas station or using someone's schrader-only pump.
I've used this to get a little more valve stem length when helping someone out using a short valve stem with taller rims. It weighs so little that you won't notice it in your saddlebag.