Zipp: Works with Zipp butyl inner tubes with a removable core as well as other leading tubular tires and inner tubes that have removable cores. (Important note: These integrated extenders are not compatible with some older model Zipp Tangente Tubular Tires. Those tires use the older Zipp Valve Extenders.)For ease of use the core is located at the end of the valve extender. Made of lightweight aluminum, and featuring an integrated air seal, the extenders are designed with the same attention to detail and performance that s built into Zipp wheels and other products.