It's probably a question that has been asked before, but I'll ask anyway. I noticed that OS offers ringed and non-ringed glow engines of even the same series. I'm assuming that the non-ringed engines have the tapered sleeve/cylinder instead. I'm assuming the ringed engines have piston rings like that in a car engine. Right? Because there are both types of engines, there must be advantages to both. Right? Help me out here; what are the advantages of both? Or of one type over the other? Why are both types of engines out there? Thanx. Jim