I just finished building up an inexpensive frame I acquired. I built it up initially as a single speed to check the fit before deciding whether it is worth spending money for a good paint job. Before I decided to go SS for the time being I did try to mount a standard off-the-shelf Dura Ace rear der that was on my Bianchi. The mounting bolt hole on the new frame seems a smidge too small. Are there different size mounting bolts?