The Phillips head has pretty much replaced the flat head when it comes to automotive screws. It is easier and faster to work with, and can be tightened more than a flat head with less chance of it stripping the screw head. You should have a number of different Phillips head screwdrivers in your tool box, you'll be using them all the time.
When choosing which Phillips head to use for a job, pick the size that best fits the screw you are working with.
Check out a picture of a Phillips head screwdriver.
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