Use the larger external jaws to get external measurements, such as screw lengths or screw head diameters.

Open the jaws wide enough for the object being measured to comfortably fit between them.

Gradually close the jaws until both sides touch the object. Don’t push too hard, yet firm enough to make sure both jaws sit flat against the object.

Check that your object isn’t crooked when you take your measurement.

Read the measurement.

Take the measurement a few times and make sure it's the same—or very close—each time. If you get inconsistent readings, zero the calipers and try again.

Zero the calipers before making another measurement.