What is the difference between 922 and 921 bulbs?

When are drum brakes better than disc brakes? How do you check if a car odometer has been rolled back? How much to sell used tires for? Can you use a 1400 mah battery to replace 500mah battery? What does an oil check light look like? Each cell in a typical car battery has a little over what volts? Does a 01 mustang have anti-lock brakes? Will a fuel pump cause a catalytic converter to go bad? Does a Mazda etude 2001 model have a fuel filter and if so where is it located? 1988 Ford E-150 with a 4 9 L V6 engine having electrical problems The battery will not hold a charge after turning off engine And engine idles up and down when runnig? What does a key fob do? How do you use a fuel line disconnect tool? Where and What kind of wires are needed to replace the cables for the battery terminals? Where is the fuse box on a Renault Espace? What is the minimum thickness of car brake pad allowed for safe car driving? Why does your Diesel engine smoke? How do you turn up horsepower in a 5.9 Cummins? How do you remove a Toyota Yaris bumper? Do you have to have a yahoo account to log in into yahoo messanger? Advantages of desktop computer?

What is the difference between 922 and 921 bulbs?