Correct measurements of any tight tolerances are a necessity to ensure the proper operation of your mechanical and electrical equipment. Feeler gauge blades have the width -- in metric or standard units -- of the blade stamped near their base. When using a feeler gauge with only metric sizes stamped on the blade, you can still determine the standard size by converting the metric dimension. A simple mathematical equation allows you to precisely convert a metric dimension to a standard equivalent.

Slide one blade of a metric feeler gauge into a mechanical gap to determine the gap width. The correct blade will slide into the gap while slightly contacting the top and bottom of the gap.

Read the number stamped on the bottom of the feeler gauge blade matching the size of the mechanical gap.

Enter the metric measurement into a calculator. Multiply the metric number by 0.039 to convert the metric dimension to standard units. For example, a feeler blade 3mm thick multiplied by 0.039 equals 0.117 or 3/32 inch.