Normal level on this type dipstick is anywhere within the checked area. DONT overfill as it could create a problem with seals. Your tractor will operate fine anywhere within the limits of the checkered area. As for screwing in or out, I suppose it is up to you, but I would not fill it to the upper end of the checker area if you check it with the plug unscrewed as the level might be a little too high. My 4220 takes about 1.5 gallons of oil to fill from low to high mark and it hold 6 gallons total. SO I have plenty of oil left when it is not even touching the stick. Problem with not touching the stick is that you dont know how far from the stick it is!!! So I check mine occassionally and top it up everytime I burst a hose.