The MM3 has three rollers. Two rollers are fixed in place and the third roller is adjustable. The roller sits in a cam that is firmly in place inside the housing. The cams have a slightly off center bushing approximately three one-hundredths off center. This gives the roller some adjustment within the given range. The cams can then be set with set screws.
The problem that I am having is that there is no external way to tell the positions of the roller. I mean it's not going to be perfectly set but if I could quickly select my grind without looking inside of the mill I believe it could be a time saver. As you can see on the left the third roller can be adjusted from a very wide gap to a very narrow gap between the roller and the grind wheel. The gap is measured with a feeler gauge and the cams are set by set screws.
The Feeler Gauge is a neat little peace of hardware that you can get at any reputable auto parts store. The cheapest one Autozone had was 2.99 and worked for all of the gaps I could possibly need. The tool is made up of strips of thin metal in several different thicknesses. If the gap you want isn't a size (such as .065"), no worries, just use two or more strips and add the thicknesses (you could use .040" and .025"). When you have the cam's adjusted you can turn the set screws to lock the third roller in place. My malt is set at .040 inches. This is a fine grind that yields excellent extraction.
You may also have noticed that accessing the inside of you mill is impossible with the standard hopper and base attached. No worries! If you make a cut where the red arrow is in the diagram to the left You'll be able remove the piece of metal and change the gap when you remove the set screws. This isn't ideal but without some sort of removable plate option or a better way to get at the inside it's going to have to work. I'll keep thinking about it and post my solution eventually.
The grist produced by this mill is superior. The grain bed was dense after vourlafing and the sparge although slower was never in any danger of being stopped. The accumulation of grain particles in the bottom of the fermentor is minimal. When I dumped the grain after my last mash the grist had formed a near solid chunk that pulled away from the sides of the tun in a solid chunk showing the compaction.