This is the Elephant hide loop model from African Sporting Creations.
Belt is their medium. From the center of the buckle to the first hole is 40.5". 46.5" to the last hole. Holes are an inch apart, and there is easily room for a hole at 47.5" and also at 39.5".
Remember, you are wearing this over everything else, and not too tight...so they need to be sized a little larger than you would do a normal belt for your trousers.
Used only at the range. If you want to use on a smaller cartridge, you can spray the loops with water and put the belt in the sun to shrink. But the danger is usually having the loops too tight, and you can't freely extract the ammo in a hurry! :) Will also work as-is for 500 NE. Would need to be shrunk a bit for 450/400 or the .458 belted magnum family of cartridges, as they pretty much just fall in right now