For different coffee brewing methods you need different size of coffee particles. It is important to get the best taste possible.
There are 7 grind sizes.
Extra Coarse (10)
Looks like peppercorns. Mostly used for Cold Brew.
Coarse (8-9)
It is similar to coarse sea salt. It is ideal for French Press, Percolator or coffee cupping.
Medium Coarse (6-7)
Looks like rough sand. Perfect for Chemex.
Medium (5)
Similar to sand consistency. Acceptable for AeroPress and Siphon.
Medium Fine (3-4)
Looks like table salt. Also good for and for pour over coffee drippers.
Fine (2)
Finer than table salt. It is ideal for Espresso Machine and Moka Pot or even AeroPress.
Extra Fine (1)
Looks like cocoa powder. Turkish and Greek coffee.