Hi everyone, Thought this info might help someone else. I just got my G20 and wanted to transfer the roof rack from my E92 to it. Initially I found that the anchor bolts needed to be larger (as most have found here) I can confirm that that a M7 x1 20mm length worked very well. I did have to chase the thread with a tapered tap to clean out the hole (very light cutting) I also had to tweak the distance between the feet of the roof rack a little to get it to line up well but that was easily accomplished by loosening the screws on the underside and adjusting to fit. Sides closed well and locked and of course the sun roof also clears no problem (wasn't really a concern)
So to summarize
M7 x 1 SHCS 20 mm long and chase with a tapered tap for installation.
Hope this helps someone else !!
I happen to buy the M7 screws on amazon, not easy to find and
griped about the price a bit but they worked well Link below
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1