The .2 and .4 refers to the resistance, which is measured in ohms. The lower the ohms, the more power it takes to heat it up and the faster your batteries are drained. More surface area (thicker wire) = more vapor production and lower ohms. Get too low and you have a dead short, which is bad. Kablooey bad. If you make your own coils, learning about ohms is a must. Even if you don't make your own, it'd still be a good idea to learn.
316 refers to 316L, which is a type of stainless steel. 316L stainless is medical grade and is popular in fashion jewelry, body jewelry, etc because it doesn't rust. There are lots of different types of wire used for making the coils that are used for vaping. The most commonly used are: kanthal (A1 grade), stainless steel (grades 304, 316, & 317), titanium (grade 1), Nichrome (series 80), and nickel (Ni200). Kanthal and Nichrome will work with all mods. Stainless steel, titanium, and nickel require mods that have temperature control feature.
Types of coils (single, quad, etc) refers to the way the coil is made.
Hope that helps
