Mar 09, 2015· How To: Adjust the Mill Gap of a Barley Crusher. March 9, 2015 Written by John. ... After loosening the screws, just turn the knobs on either side of the mill to adjust each side of the roller gap. Put the feeler gauge into the gap as you adjust the knobs. You want the feeler gauge to not be stuck in the mill, but also not be completely loose.