| If you know anyone with a thread gauge, that's the easy way - but you need a screw to figure out what size they are...
Assuming you don't - take the pedal (or the screws if you have them) to the hardware store - a good hardware store, the kind that have drawers where you can buy single screws.
Go to the metric section, and grab an M2.5 or M3 Flat head screw. When you have the right size, the screws will go in with your fingers, without a screwdriver. You want to make sure they will go in with fingers or you might be forcing in a screw with the wrong pitch, and that will wreck the threads in the enclosure.
It's possible that they used a weird thread pitch, in which case you may not find what you need.
Total long shot, but if the metrics won't fit you might find an SAE 6-32 will fit. Many pedals are built with Hammond enclosures and this is the size screw they use.
My octabass is at the studio or I'd measure it for you.
Monk | 
