Ok, here's the design that was the most fun to make. I had allen wrenches once long ago that had a cool holder with two angular ranks of slots for a full range of sizes. I've reproduced it here with the addition of the peg board mount.
SAE or Metric? Neither. I've made the holes tight for whatever type of allan key is inserted. I printed two and then used a drill to resize the holes for a good snug fit. Now once I had done that, I could have measured the holes and then rebuilt the model, but I didn't bother.