The Carrera "Special" guide that works for Non-Carrera brands of track with a narrower (than Carrera) slot. The part number is 85309 and it's used for 2007 and newer cars.
The Carrera "Special" guide in the packaging.
The standard guide on a Carrera Scirocco.
The "Special" guide now on the Scirocco.
Both guides, the standard guide on top and the smaller guide on the bottom of the picture.