I'm lead to believe that there are 'different' Silverstone sets out there.
Some supposedly have / used 14mm bolts (Same as our RS's)....and some used 12mm bolts [Hence i've seen a few who've bought these have had to drill out the holes to 14.5mm for example to accept Clio bolts !].
I also believe there are two different off-sets available.
The fact there is a different centre-bore size out there in these doesnt surprise me..........