For a quick measurement of plastic parts, a so called caliper is used in general.
This distance measuring device has one stick with two outside and two inside measuring legs.
The top ones of the measuring legs are fixed, while the bottom ones are movable.
Additionally, some calipers have a measurement rod to measure the depth.
With outside, inside and depth-measurement more or less every tolerance of a plastic part can be checked.

A difference in calipers can be found in how the measured values are displayed.
There are three different display types available:
– Ruled scale (Vernier)
– Dial
– Digital

It has to be noted that especially for soft plastic (like TPE), a too high pressure on the movable measuring legs will distort the measured value.
Furthermore, the measurement at small supports may lead to a tilt and hence a distortion of the measured value.
These are the reasons why, after the first measurement with caliper, additional measurement devices are necessary for exact measurement.

For example: A testing pin is better suitable for the inside measurement of a plastic part.

Caliper in Plastic Industry by KDP
Caliper in Plastic Industry by KDP

Image 1: Measuring technology: Calipers with vernier and digital display.
Image 2: Measuring technology: Caliper with dial display.

Related topics:

Measuring technology

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This glossary of plastic industry is provided by PLEXPERT Canada Inc.