What makes the difference in a G,H,M models of the motor graders.
No sure I understand the question for sure, but the letter indicates different generations of cats. Like Ms is where cat started using pilot controls.
What brand are you talking about? Cat, Deere, etc?
Cat machines I am referring to as size 14H, 14M, wanted to know how the letter sized the machine.
The number is the basic size. The letter basically tells the age, not the size, though sizes do change slightly with redesigns. Every time they make a major model change, they change the letter. If you have questions about specific models, we can give you general answers on here. Your best bet is to get a hold of a "Caterpillar Performance Handbook". You can get used ones on ebay. They have all the specs for current models and old ones. Generally
I have find a site where are some informations about some types from Caterpillar: http://www.ritchiewiki.com/wiki/index.php/Category:Caterpillar_Motor_Graders