Basiclly all of the above. It's pretty vague and no body has really given me an exact defination of what they are. But to give you some examples: Class 5 JD 9550, Case 2366, Tr88 NH, R52 Gleaners, TX64 NH Class 6 JD 9650CWS, JD 9650CTS, JD 9560 STS, Case 2388, TX 66NH, TR 89 HH, R 62 Gleaners..... Class 7 JD 9750sts, R72 Gleaners, TX 68, 480 Cats, TR 99 Newhollands..... and the lists goes on. Obviously there is some variation within classes as to what machine will out perform its pears in certain situations. But as I understand it (and I stand to be corrected on some of those class ratings) that should give you a bit of an understanding as to what combine is what. I hope it helps a bit.