The knurled nut on the outside is supposed to be installed tightly. That way, you can make adjustments with it. You align the wheel using the Mark I Eyeball and the QR, then run the adjuster screw in with the knurled nut (or turn it out as needed). The head of the screw is against the axle and serves to hold the spring in place. The only time a screwdriver is used is for the initial installation and to install the knurled nut. We used to booger up one thread so that it would go on tightly, but then they invented Loctite.

Once set, it is pretty much set. I have been running around with one missing knurled nut for decades. I recently found a replacement, but it looks out of place because it's sorta shiny.