Like a stripped cable anchor bolt. That elusive bit kept me from finishing my project: A 1991 PDG Series 5 with all the original 105sc components except for the pedals. I never thought it would be so difficult to find something so simple... and after all my failed trips to the LBSes, I never thought I'd be as happy as when the mechanic brought out this grimey little bolt and said "You can have it for free. It's was just in our old parts bin."