K2: internal adjustment type with the best efficiency, with 48mm hexagonal stainless steel burrs. The standby machine for novice entry is enough for daily use. K4: externally adjustable, with 48mm hexagonal titanium coated stainless steel burrs. It is mainly ground into espresso, assisted by pouring coffee. K4 is an option for people who like medium and deep roasted coffee beans to show a sweet taste. K6 multi-purpose all-round external style, with 48mm heptagonal stainless steel burrs, mainly poured coffee, supplemented by espresso, good for light roasted coffee beans, with clean flavor & sweet and sour fruit taste.