Originally Posted by 
Dougal
				
			 
			Yes that's the same change I'm talking about.  I use the terms metric and imperial because the older hubs used either 7/16" or 3/8" bolts (can't remember which) to hold the drive flanges on.  The later hubs use M12's.
AFAIK the change came about when the hubs were redesigned to take ABS (sometime around 1992) and became standard on everything even if it didn't have ABS.  Some people talk about 10/24 spline changeover but the changeover in axle splines wasn't consistent, there are some metric hubs with 10 spline axles attached.
I think there are three different caliper bolts, M12, M11 and an imperial as well.  IMO they're interchangable for those of us who own drills.