Do you have deep cross section rims' When you air up your tires, is it a headache to get your pump to bite on the end of the presta valve' The Zipp Valve Extender is the answer. The extender threads onto the end of your valve to give your pump more surface area to grab. These are black anodized aluminum with a laser etched Zipp logo and a 3mm hex key fitting in the pump head end.They will fit any presta valve stem and work with both clincher and tubular tires. Zipp Valve Extenders come in five sizes 27mm, 33mm, 48mm, 74mm, and 98mm. Please Remember: Before installing the Zipp Extenders, make sure to open the valve on your tube by unthreading the valve needle nut and back it out tight, lest it should vibrate back to a closed position. Zipp recommends using Teflon plumber's tape on your valve stem to create an airtight seal with the valve extender. Also, please note that the price is per extender, not per pair.