According to the first hit on a Google search:
"The Tinsley Thickness Gauge dry-film thickness measurement is designed for measuring the dry-film thickness of any non-magnetic material such as paint, plastic, etc., or plating such as zinc or chromium over a ferrous base (iron or steel)."
The picture which is alongside this quote shows a virtually identical instrument.
John
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Edited By John Hinkley on 06/01/2023 12:39:46