I have been googling for a few hours but to no avail. The problem I have is that I am trying to install an outdoor fixture on a new surface mount junction box. The screws included with the light are size 8-32, but the screws on the box are very slightly larger. They aren't 10-32 (those are too large) and I can't find any information on what size the screws are supposed to be on the box. This is the fixture I'm using and this is the box.

I believe they are 10-24 course thread.

10-24 they are. Make sure you get stainless steel screws. It will save a lot of work when you replace the fixture ten years from now.

Seconded on the stainless steel, Nothing is more annoying than getting a rusted steel screw out from a tapped cast aluminium hole which is what most of those surface boxes are made of.