Online caliper
An on-screen caliper for small, precise widths: the thickness of a coin, the diameter of a screw, the width of a bead or a wire.
How to use it
- Hold the object against the screen with one side touching the fixed jaw A.
- Slide jaw B until it just touches the other side.
- Read the width on the display, or in the box beside the caliper.
Drag the steel beam to move the whole caliper. Use the round handle past the end, or the 0° and 90° buttons, to turn it. Setting it upright helps for things that are taller than they are wide.
Why use a caliper instead of the ruler?
For small objects, the jaws are easier to line up than marks on a scale. Two flat faces meeting the edges of an object leave less room for guesswork than judging where an edge falls between two tick marks. That's why real calipers are the standard tool for screws, wires and drill bits.
Getting an accurate reading
- Calibrate first. On an uncalibrated screen, a 5 mm reading can easily be half a millimeter out, which is the difference between an M5 and an M5.5 screw.
- Measure across the widest part. For a screw, that's the outside of the thread.
- Look straight at the screen, not from an angle.
- Measure two or three times and take the middle value.
A screen caliper gets you to about a millimeter. If you need tenths of a millimeter, for engineering work or 3D printing tolerances, use a real digital caliper.