Currently on my car I have borbet RST's but no centre caps. The wheels are prety hard to come by anyway and finding centre caps for them is proving ni-on imposible! I've tralled German ebay and everything.
I have however noticed that they come with two centre cap possibilities, one attaching like the borbet A centre caps do with a hex bolt thingy. Obv these are easier to come by, thing is when I look at my wheels they dont seem to have any sort of fixing point for the bolt.
I was hoping someone could perhaps post a pic of how a type A cap attaches to the wheel or if anyone knows if any other caps would fit!
Here are some pics.....
Borbet RST

With flat caps

Cap comparison (off a german ebay add)
