My neighbor and I have added a little twist to the common cancelling rule: Green gets one washer in the 5 hole: 5 points, Green Then, Red gets one washer in the 5 hole: Points cancel Then, Red gets another washer in the 5 hole: 5 points, Red. -5 points, Green. This rule is recommended only for very good-natured players!
Well my set is covered in used conveyor belt, as is the fashion in northeastern Minnesota (lots of miners). I can tell you it adds a lot of excitement to the game. I can post pics if you're interested.