The 6mm bolts are 90 in-lbs (that's about 8 ft-lbs.). The 18mm nut is just tightened enough, like 8 ft-lbs, to allow the locktab to get a lip over one of its flat sides to hold it still. In operation it only holds the oiler adjuster screw in one place. If you try to tighten this skinny 19mm nut very much, it will round off and leave you in a world of hurt for trying to get it off again later.