Some of the expensive ones at auto store are meant for heavy duty use. (taxi,company car, emergency vehicles) They just have a thicker filament in the bulb. If you run over a lot of rough roads or have unbalanced running gear (see Andy), these are for you. These are also more forgiving if you have an older battery charger that will ocasionally put out over 13 volts. Kinda like the rough service lightbulb at NAPA for a lead light.
"Sometimes I wonder if the world is being run by smart people who are putting us on, or by imbeciles who really mean it." Mark Twain
AIR 22749 WBCCI 2349 NOVA TAC TN-6
1989 345 LE Classic Motorhome