The UMI thrust bearing kit is made to sit between the spring and the spring seat on Viking and UMI coilovers, allowing the spring seat to rotate easily for smoother height adjustment. It’s recommended for easier turn-down of the spring seat but not strictly required for installation. UMI advises against adjusting vehicle height on the car without using a thrust bearing kit.
UMI Performance Thrust Bearing Kit Viking Coilovers & UMI Coilovers