How to Figure out Screwdriver Size. Finding the right size of screwdriver that you need makes your construction or repair job much easier. Screwdrivers and screws come in all sorts of shapes and sizes. Here's how to figure out which screwdriver size you need.
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Check the package. Match your screw size with your screwdriver size. If you have the package in which your screws came in, look at the package for the size of screws you bought. You want to look at how long and thick the screw head slot is. You can then find a screwdriver that's the same size.
Look at the head of your screw. A Phillips blade will have a blunt tip and the screw slots will curve where they intersect. A Torx blade will have a star-shaped tip for screws in appliances and garden equipment. A square-drive screw head will not slip despite strong twisting.
Measure your standard blade screw head slot. You'll want to use a tape measure to determine how long the slot is and how wide it is. If you use a screwdriver that's too wide and too thick, you won't be able to fit your screwdriver in the slot. If you use a screwdriver that's too narrow and too thin, it will slip off easily.
Use a screwdriver with parallel sides for wooden screws.
Use special screwdrivers to install screws in awkward spaces. You should use a stubby screwdriver if your space is limited. Use grips for screws that are in deep holes.