To lock down the ribbed drive belt during installation or removal of the VISCO fan.
A 100% secure locking can occur without damage to the drive belt disc or the aluminum housing.
No sliding of the tools, and therefore no danger of injury.
Audi A4 1.8L and A4 1.9L TDI, VW Passat 1.8L 20 Ventiler (ADP, ADR, AFY, AEB, AFN)