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Measuring Screw Gauge

When measuring the Self Drilling Metal Screws (with a drill point), the gauge should be measured from the drill point or between the thread as per this image from Hobson.


tek screw

For other screws, including Self Tapping, Wood, and self Drilling Timber Screws, the gauge is taken as a measure of the major diameter of the screw, as per below.

Thanks to Hobson Engineering as a source for the above and below information