Metzeler Tire Tubes Features: All Metzeler tubes are made from natural rubber and feature heavy-duty construction for excellent service and puncture resistance All valve stems are TR type Tr-87 metal 90-degree valve stem (standard length) Tr-4 /Tr-6 metal center valve stem Tr-4 uses an oval-shaped transition from valve to the body of the inner tube Tr-6 uses a round interface Metal valve stem construction with lock nuts Note : Tr-4 and Tr-6 valve stem styles can be used interchangeably.