is that V belt? if so just follow this formula to get a Gates belt of the right size

67=3/8" Width

68=1/2" Width

69=5/8" Width

just measure what you will need with a string to get it's length

then take your belt width, it's probably 5/8" so 69, that's the first part of the part number, then take your length and add it to that number, so if you need 50" just order a 6950 belt, pretty simple.