The newer models of the Walther Q5 Match, Q5 Match SF and Q4 Tac use a numbering system on optic mounting plates. This Red Dot Mounting Plate Guide video shows which plates fit which optics.

1. Docter/Vortex/Burris/Meopta (various other imported optics)
2. Trijicon
3. Rear Site (Mounted on gun at time of purchase)
4. Leupold / RMS