How they're machined makes normal disc brakes not fit. When I say normal, it seems like they're all are now pm with an IS adapter, and the design of adapter doesn't fit as the holes don't extend out.
Example of the adapter shown in the link for Avid BB7 brakes
https://www.google.com/search?clien...ih=214&dpr=3#vhid=tjp9qXBxcjHI0M&vssid=mosaic
Example of the adapter shown in the link for Avid BB7 brakes
https://www.google.com/search?clien...ih=214&dpr=3#vhid=tjp9qXBxcjHI0M&vssid=mosaic