Understanding Fastener Measurements

In the examples below, the first number represents the diameter; if there is a dash, the next number will represent the threads per inch or thread pitch; the last number is the length of the fastener.
Example: Size 6 x 1 flat head phillips wood screw	Definition: 6 = the diameter x 1 = length
Example: Size 1/4-20 x 1 1/2 hex head caps, zinc plated	Definition: 1/4 = the diameter 20 = thread pitch or threads per inch x 1 1/2 = length
Example: Size M6 1.0 x 25mm hex caps, zinc plated	Definition: M6 = the diameter 1.0 = thread pitch or threads per inch x 25mm = length