i want to set up my mountain bike with a hub dynamo. i found a schmidt hub dynamo for disc brakes on the peter white cycles website. it's the one for disc brakes. i have a gary fisher mountain bike with hayes mechanical disc brakes, & i was told if my disc meets the iso spec it will fit this hub dynamo. what's a iso spec disc? what does that mean? my disc bolts on with 6 screws, & the schmidt hub also has 6 holes for a disc, but i want to make sure it fits.