U-Shaped Shims - Designed for quick removal and installation into tight stacks and locations where twisting the shim into the stack is not an option or when the car is on the ground. Commonly used for fine tuning the suspension. Semi-Solid Shims - Designed for quick removal, providing a secure installation that will not fall out yet requires 3/4" of space to install or remove. Typically installed when the vehicle is off the ground. Commonly used for fine tuning the suspension. 2-Piece Collar Shims - Designed to attach around the shaft of the shock and secure in place with a zip tie. Commonly used during initial set-up or to take up a large amount of travel.