Manufacturers interested in supplying their products globally are being urged by the U.S. Commerce Department to join the transition converting from inch standards to metric standards of measure or international System or Units (SI). An earlier study found that one-half to two-thirds of U.S. exports are "measure sensitive" causing potential foreign purchases to be placed with countries using the metric units of measure. Since the metric standards can be very involved, we will cover only the basics to familiarize you with terminology and help in the conversion from inch to metric. Currently throughout the world, many metric standards are being used:

Many of these metric standards have specifications that are very similar to one another, but some dimensions are not directly interchangeable. The availability of DIN standards has influenced its popularity, but with the adoption of a unified measuring system, ISO is becoming more and more popular, especially with the introduction of ISO 9000.

To determine the diameter of a fastener, use the above conversions then round to the nearest whole number.

The length can be multiplies in the same way to determine the length in millimeters.

THREADS

Metric fasteners also have a course and fine thread series although most fasteners are supplied in the course series. The exceptions are hex head cap screws, socket cap screws and hex nuts which are available in coarse and fine series. The coarse metric has more threads per inch than a course threaded inch standard fastener and therefore has a larger stress area. Fine thread metric fasteners also have more threads per inch than the fine threaded inch standard fasteners and an even greater area of stress. To avoid stripped threads, it is recommended to use a thicker nut more thread engagement and greater reliability.