The lower thermostat opens around 250 degrees, then closes after a rather long cool down period, the upper thermal fuse blows at 350 degrees, so for "normal" conditions, it never sees 350 degrees. In the event of low airflow, or a fire, or defective lower limit thermostat, the upper thermal fuse will blow.
Most of the time, the lower limit thermostat just failed to open due to a trip temperature above 350 degrees, thus it must be replaced. They both come in a kit for these reasons.
In the event of nuisance repeat fuse blowing, I have put a bunch of limit thermostats in an oven, selected the one with a lower trip temperature and the problem was solved. In these cases, however, I never found the problem as the measured air flow and cycling thermostat temperature all where "normal". Suspect customer overloading, or the use of fabric softener sheets that clung to the back vent. I also suspected a batch of out of tolerance thermal fuses, but was unwilling to destructive test a bunch of them. Also, I have discovered erratic cycling thermostats, mostly the heated ones, and erratic, high turbulence venting.
In view of the above, anyone doing dryer repair must have a decent airflow meter or manometer and a accurate digital thermometer.