These axles are specifically for Gen 2 ISO-DH Needle Bearing rear hubs with serial numbers starting with 291. They will not fit Gen 1 ISO DH hubshells with serial numbers starting with 191. PHB578 150mm x 12mm PHB579 150mm x 10mm PHB580 157mm x 12mm Axles are equipped with a Needle Bearing race. This race needs to match the tolerance that is marked on the outer race within the driveshell. The end cap seal for the Needle Bearing driveshell is marked with the race tolerance, a number from 2 to 4. Please input into your order notes the number marked on your driveshell seal (or the original axle) so we can match the tolerance.