2 Piece Grinder:
The 2 piece grinder just grinds the herb. It comes with two halves to shred the weed and that’s just about it. When the resin builds up, you’ll get keif which you can just brush out after continued use. This method of collecting kief isn’t ideal, which is why I recommend the 4 piece grinder. 4 Piece Grinder:
The 4 piece grinder grinds the herb, and collects keif through a screen. There is a compartment that stores the kief, which you can then scoop it out if you want. Personally, I think that these grinders are usually better quality and keeps your kief fresher.