This part is not a special optional part, it is a steel shim that is used as a standard for the gear differential of the kit. It is a shim that is also included in the gear kit 's maintenance kit, but why dared to release it separately, it appeared as a part to add to the standard gear differential.
In the kit standard, this shim is included in the outside of the small bevel gear (10 T) inside the gear differential, but this is the proper value as a clearance for normal smooth operation. However, by daring this shim in two places and making the backlash tight, usage that increases the differential response response may lead to time-up. Especially effective is a tight turn of a technical circuit and a quick turn back chicane etc. It is possible to increase the acceleration response after clipping and lead to time-up.