Axial thrust bearings are designed to go between the spring and spring seat to prevent spring bind when adjusting height as well as during turning. When you hear the BING-BONG when you turn the wheel while parked, that’s your spring binding.
Bearings are sized based on the ID of the spring. If the coilover spring has a 60mm ID, you should be ordering the 60mm thrust bearing.
Thrust bearings are sold “set" (one bearing, two washers) per corner. Order a quantity of 2 if you need a pair. It is recommended that these be installed with a coating of bearing grease on the needles as it prevents moisture build up.
