I have a 2002 year Trek 4300 Alpha. It seems to have typical four-hole chainrings but I have honestly tried six sets of allen keys (imperial & metric) and none fit. 4.5 mm is the closest I've found but it's not QUITE snug enough on all holes and will definitely strip all the holes. Maybe 4.6 would work or 4.7mm. 5 is too big and will not fit. So then I go to Imperial but 3/16 is too big and 5/32 definitely too small. This is absurd, what the heck allen fits these? I'd drill them out but I'm sure any replacement screw would be off by some miniscule fraction of an inch!