Blades come in "F" styles and "S" styles, which is finishing, and skip tooth respectively.
As a groomer, I prefer "F" blades exclusively, even for prep work; skip tooth blades were designed for prepping in mind, but they can catch skin too easily IMHO, so I just don't use them; "F" blades do all the work just as well, without having to have two types in your box.
Agreed Sophie. Skip tooth blades are rarely a better choice over a finishing (full cut) blade. F blades are much safer, and give a better, smoother finish anyway. Here is a picture of both, so everyone can see the difference, and see how easily skin can be caught in a skip tooth blade. These are both 5 blades, so they leave the same length.