Grain Mill Roller Gap ?

From monster mill:

Roller Gap:
Leave the roller gap where it is to start! Most of the milling will be very close to, or a little tighter than the factory setting. The adjustable gap is set at 0.045” on all mills when they are assembled. The thumbscrews on the mm2/mm3 are tightened by hand, and should not be loose when you get the mill. The screws on the mm2-PRO/mm3-PRO should be tight. If the adjustment knobs will turn when you receive the mill, then the screws may have loosened during shipment, and you will need to check the gap setting. Feeler gauges work well. As long as the screws have not loosened during shipment, make a small mark on the frames before changing the position of the idler roller. A center punch or a sharpie work well.
Adjusting the gap:
Once you have brewed using some grain that you crushed with the factory gap setting, you’re ready to adjust the gap and turn up the efficiency of your brewery. A gap of .045" will produce a medium crush. .055" turns out a coarse crush. .038 to .040” should provide a great fine crush with great extraction efficiencies. Experimenting with different settings can improve yields. Recipes including wheat and rye sparge easier with a coarse barley crush
To adjust the gap, loosen the screws so the knobs can turn. Use a feeler gauge to measure and set the gap. Slide the feeler gauge shims into the gap on one end of the rollers. Tighten the knobs so the feeler gauge is tight in the gap. Repeat on the other end of the roller to be sure they are parallel. Tighten the screws on the
adjustment knobs. Tighten the thumbscrews on the mm2/mm3 mills by hand as tightly as you can using your fingers. The rounded end of the thumbscrew should grab the matching groove in the knob, and keep it from moving. If there are any problems with the knobs coming loose, use a small set of pliers to tighten the thumbscrews. DO NOT OVER TIGHTEN.
The gap should be measured at the bottom of the rollers for the MM2/MM2-PRO, and between the top DRIVEN roller, and the bottom roller on the MM3/MM3-PRO (as shown in the diagrams). The grain will exit this gap straight down on the MM2/MM2-PRO and at an angle when milling on the MM3/MM3-PRO. When setting the gap on the 3-roller mills it is important to make sure that you set the gap such that the bottom idler is furthest away from the top non-driven idler roller. It is possible to set the same gap spacing with the knobs in two different positions. This will not mill the grain properly, and the mill may bind.