Do the genuine Mini attachments for the racks fasten to it, using a tee bolt or something similar? Or do they just clamp to the bar the way most Thule and Yak stuff does?

I'm about the order some rack stuff and it occurs to me I have no idea how they work. I got a lot of older Thule accessories made for the square bar that I'd like to figure out a way to use, but it doesn't look like it'll be easy.

 

Yes, the slot is for the attachments to slide into. The key you were (hopefully) provided with your roof rack unlocks the sides, which hinge down and allow you to remove the rubber strip inside and slide your attachments in. A great system if you ask me, I love mine!

 

The MINI Rack bars are made to the same shape at the Thule Aero Bars. Check with your rack dealer and see if they can hook you up with the "Adapter Kits" for your older rack accessories to mount them to Thule Aero Bars.

 

True, BUT... :-)

the "slot" in the OEM roof rack is larger than the one on Thule racks. My rack vendor was able to provide me with larger T shaped attachments

 

That is odd my bars are "EXACTLY" the same as Thule Aero Bars in every measurement.