I also use the #40, with no master link. I was using #41, but some times your rear tires will leave the ground. This happened to me. When it does it puts a lot of tension on the chain and it snapped. So I stepped up to #40 and so far so good. Now I hope that I don't tear up a transmission. As far as sprocket sises 12 tooth transmission and 46 tooth axle is just about the best combo to use. You can run a wide verity of tracks from long to short and even do some drag racing (On Dirt). Witch is a whole lot of fun. Oh and George, we might be doing some drag racing in milledgeville. So I hope that You, Larry, and Jeannie can make it out some time.