One of two things is likely happening:
1: you used loctite on your screws and the loctite is eating the disc causing it to fracture.
2: you aren't using the mounting washer that Union supplied causing a greater load at a more localized point. (point load).
if it's neither of these two; i wouldn't know what to tell you. Union's disc are made of a very robust nylon. your best best is to call the shop that you bought them from or Union / Union Distributor.
Last edited by BurtonBindings; 02-12-2013 at 08:18 AM.