I suspect they're designed to be used with brakes that tension the spring internally within the brake arm rather than using an external hole.
What type of brake works like this and will I need to change the bosses?
@Fluffychicken, Your probably right about the On-One set up as the silver bits are a little too deep. I could do with the washer set up that's on the black canti bosses because I think that may work as I could set the positioning of them when tightening up the boss. Anybody got any lying about or do I have to trek down to B&Q and get my drill out?
Also found something interesting whilst browsing Sheldon Brown
Dia Compe style cantilevers often use a totally different approach. The Dia Compe system doesn't use the spring hole in the cantilever boss, but has a separate spring block as part of the cantilever assembly. This spring block is the first part to go onto the boss, and it has a hole for the end of the spring. When the bolt holding the cantilever to the boss is loose, the spring block can turn freely, but when this bolt is tightened, it locks the spring block in place. The spring block has flats for a cone wrench (usually 13 mm) to let you rotate it to provide the desired tension.
Can anyone shed any light on this?