【How-to】Is the m6 a 10mm

The M8 will measure about 8 mm in diameter, more likely, just a touch undersize, (.31496″) The M10, about 10 mm in diameter, (.3937″) and the M12 about 12 mm in diameter, (.4724″). The “M” designates the bolt is Metric and the number after the M indicates the size. The number after that is the length.