I am replacing the original pads in my Cane Creek SCR-3 brakes, with Shimano. The Allen head in one of the original retaining screws is rounded out. Probably damaged during assembly, I've never touched them. I got the screw out with pliers, and expected to replace it with one that came with the new pads. But the threads are different... look identical to the eye, but the Shimano screw just won't go in. The pads are compatible but the screws aren't? Nobody told me that.

I guess I can put the old screw back in with the pliers, but I should get some replacement screws that will work. How do I figure out what I need? Will a shop know what to give me? Or will they have to fumble through their big box of assorted nuts and bolts?

you could just force it in and cross-thread it if you don't care about the pad holder.

You actually don't even need the screw there to start with, because unless you're going backwards at quite a pace, they'll never fall out.
That's how campagnolo cartridge pads are. They just slide and wedge in with no stopping screw.

No chance. It's a 2 mm Allen head screw, I'd snap off the wrench.

Not much interest in this topic, it would appear.

Contact Cane Creek directly. They're usually quite good about these types of things.

A good small hardware store will have it.

I emailed them over the weekend, no reply yet. In the mean time, I did put the old screw back in with the pliers. Next time I have the bike at the LBS, I'll try to remember to ask about this.

You may be able to temporarily salvage the damaged screw by cutting a shallow slot across the head with a hacksaw blade. That will let you remove and replace it with a screwdriver. As AEO noted, the screw isn't needed unless; 1) you install the pad holder backwards with the open end facing the front of the bike or 2) you ride backwards and apply the brakes hard. Neither case is likely.