Metric threads have a different callout then US (inch) threads. Metric threads specify the pitch while US threads specify number of threads per inch.
M6 x 1 ( 6- nominal thread diameter in mm, 1mm-distance between threads in mm)
¼-10 (1/4-nominal thread diameter in inch, 10-number of threads per inch)
Pitch from metric fasteners can be coarse, fine and extra fine. The pitch callout on coarse thread is often omitted. For example, “M6” thread by default stands for coarse thread M6 x 1. Thread call out that includes the pitch “M6x0.75” specifies non-coarse thread (in this case fine thread). Also all threads are right-hand threads unless otherwise specified.
Majority of standards (JIS, ISO, DIN) follow this convention.
For more information about Metric Coarse Threads please see pages 1568/1569 in the 2008 Misumi Metric catalog. Also, see the following links.
Table for Metric Coarse Screw Threads
Table for Metric Fine Screw Threads