Stiff Ring is a washer like ring that is being used to correct the position of the actual washer when it is attached to subframe.

Check out the official release from Stiff Ring team:

Stiff Ring made of special formula aluminium which used in aircraft frame building. It used to correct the car body basic geometry by filling the gap between the sub frame bolts, sub frame and the car body bolt hole. Car engine, transmission, suspension and the body shelf are mounted on the sub frame. Thus, correcting the geometry setup with Stiff Ring, the car handling will be improved significantly.   (more…)