YSS YSS SHOCK UNIVERSAL PRO X RD220-280P-04-88Thread Spring Preload or adjustable spring screw. By threading the cylindrical shock absorbers, user can turn the preload to fine tune the spring and tighten a provided bolt to fix the ring in its position, Adjustable length. It helps increase the length of the shock absorber. The two types can be upgraded to 10 mm or adjustable lengths + 5 mm., Rebound Adjustable is to control the recovery of the shock absorber. Fast or slow depending on driver needs.