I've tried googling this extensively (maybe not effectively) to no avail.

Here is the situation:

I own an older Soma Double Cross frame. It has posts on the back for cantilever brakes. Recently, I purchased Tektro CR720 to replace the current brakes. When I went to put them on, they would not fit because the diameter of the posts on the bike exceed the diameter of clearance on the brakes.

I think i'm missing something. As I said, i've tried googling it. I think I may be using incorrect terminology as there are no results that are on point.

Anyone have any advice or resources to get me on track?