In reply to top cat:
The crampons you bought are for the early versions of the 500(black and grey) and the 505(black and yellow) without the "brake Bar". The rear attachment occurs when the black locking button is turned 90 degrees and clamps onto the carbon rails. The later model 500 (grey and blue) with the "brake bar" require the crampons show in the link:
http://www.bergzeit.de/silvretta-pure-harscheisen. These crampons attach to the "brake bar" with the flip of a rectangular wire bail, they do not clamp on to the carbon rails. This style also work with all bindings in the Silvretta Pure line.
The later style crampon attachment is much preferred because you can attach and remove the crampons with your boot still in the binding. A very desirable feature! So I think you need to sell the incorrect type you recently purchased and get the proper version for your kit.
-Cheers