Like a lot of firearms the letters and numbers often do not have specific meanings and merely designate specific models eg savage 11 , but for what is worth the M suffix indicates a lightly engraved silver colored receiver, an E suffix indicates an ejector model. The trap models have steel and not aluminum alloy receivers and specials have fancier wood and engraving. The web site gives you visuals of the models and some modest information on each. h ttp://www.yildizshotgun.com/product.html Hope this helps.