Dimension 'x' is known as the circular pitch, which is equal to the circumference of the gear pitch circle divided by the number of teeth. It is a more popular method of gear pitch measure, but is not as geometrically evident due to the fact that the pitch circle is not visible on the gears.
Metric gears are another story.
It gets better. Like cutting metric threads on the 7x10, there will be very slight differences between inch and metric gears, sometimes not very significant. The only way to find out is to try out the gear in question. I'll measure the circular pitch, pressure angle, bore and a few other characteristics on some gears tomorrow morning and post the results.