Measuring your chuck makes choosing a key a simple process.
Nothing is more frustrating than losing the chuck key to your drill. Such a small object can stop your project in its tracks when you can't change your bit. If you lost the chuck, purchase a replacement. Making sure you get the correct-sized chuck avoids a second trip to the hardware store. There are more then 12 variations of chucks, so have the right information when making your selection.
Step 1
Look closely at the chuck on the drill for the engraved numbers. The chuck size looks something like: 1/4, 3/8, 1/2 etc.
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Step 2
Measure the diameter of the hole on the side of the chuck in inches with a ruler. This measurement is called the pilot shank.
Step 3
Take these two dimensions to your local hardware store to make your selection.