I just purchased a used 2003 KX-100 for my son's second bike. He is 12 and stepping up from an XR-100. I was on my way to the dealer to buy some spare plugs and masterlinks. I decided to check the chain on the bike before heading out, it's a 428. Kawasaki's web site, and a few others state that the stock chain size is 420. I realize the previous owner may have changed the chain/sprockets. His XR-100 takes a 428 chain too. I guess I could just use those master links. What is the difference between the two sizes? Is the 428 bigger (thicker) than the 420? Thanks, Steve.