This differential/spool eccentric allows you to adjust the height of the diff/spool to a new 'High' position compared to the standard kit 'Low' position. 

The smart looking piece as normal is used to adjust the belt tension, as well as being able to fine tune the feeling of the car.

Normally a higher front spool smooths the steering response compared to the standard low kit setting.

A higher rear diff can give the car more drive out of the turns keeping it flatter.  A low standard position normally gives a little more side bite.

A worthwhile item to have available to tune your Mi7 to different track conditions.