It makes me wonder if they are made in two different specifications, one for SAE and one for metric.
Yes, there are both SAE and metric prop reamers. I have and use both. But I have found a better solution. Drill bits designed specifically for drilling out props. They have a 1/4 inch pilot ground on the end of the bit to guide it. The drills come in a number of sizes - both SAE and metric. I mainly use the the 5/16 in. size. Plus I always use a drill press. The holes come out perfectly. You can find them here:
http://bennettbuilt.com/page9.htm
Bruce