Perfect pocket size, high-grade  stainless steel, gunmetal 4-parts grinder, has a diameter of 40mm. Are you looking at starting off with a radical model right away. The 4 piece crusher system is just what you are looking for.
 
A Grinder with 4 Pieces comes with a lid, sharp teeth to grind your weed to a smooth consistency, the next compartment catches your freshly crushed ganja and the 4th piece is below the kief screen and a kief catcher to collects all your fine Trichomes which you can heat up at a later stage and make small bit of hash. The compartment that catches your freshly grinded weed or to store your crushed ganja you are planning on using later on.