Martin,
Again, back in the dark ages, it was necessary to get pulleys with a "pilot" hole and then bore to suit. For belts, I used XL037 size and am glad that I did. Yes, they are strong enough for everyday tasks, but I have also found that they make and excellent "fuse" when you do a hard crash into the hard stop. I had it happen a couple of times when I had inadvertently disabled my limit switches. An XL belt is cheap insurance.