Box G313 ABS behuizing

The G313 boxes which are used all over the space have slightly funny sizes (in metric).

Which is rather annoying when you need to mount them; and round things down to the nearstest 5 or 10mm; as they are *really* 1mm off.

Sizes below:

200x120x75mm box, same story: http://www.gainta.com/pdf/g373_g269.pdf