What you receive :
 
Combo : 1 Pair of Each  2 MM & 3 MM thickness Acrylic Depth Guides
 
or 
 
Combo : 1 Pair of Each  2 MM, 3 MM & 4 MM thickness Acrylic Depth Guides 
Acrylic Depth Guides for Making Equally Thick Clay Slabs & resultantly professional earrings.
3 MM thickness is ideal size for clay slabs. 
Incase you are going to dome the earrings with resin top coat, 2 MM thickness would be the ideal size. 
Also 2 MM thickness would be best when you are rolling any clay components to be merged to your slab.
 
4 mm guides are for thick statement earrings