Tips for Measuring Metric Screws Tips for Measuring Metric Screws

The measurements of metric screws indicate the diameter size, the length and the pitch of the thread in millimeters. Millimeters are extremely small units of measure and allow for much more precision than fractions of an inch.

The Designated Measurements

The measurement of a metric screw is indicated by the letter M which is followed by a series of 3 numbers. The letter M refers to the metric unit of measure. The first number refers to the diameter. The second number refers to the number of threads. The final number refers to the length.

The Diameter

The diameter is determined by measuring the unthreaded distance from one side of the screw to the other. The measurement of the screw from outside the threads is called the major diameter. Both screws and bolts can be found in a fine pitch and an extra fine pitch design.


The precise thread measurement is determined using a thread gauge. The gauge measures one point of the thread to an an exact point on an adjoining thread. This is called the thread pitch. 


The length provides the size in millimeters of the screw, from under the head of the fastening devices to the end of the screw or bolt being measured.

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