What is traditionally called 3/8 inch glass is 10mm. Plate glass is produced to metric thicknesses even in the US. The US standard for what is sold as 3/8" or 10mm plate glass allows for a range of thickness from 9.02 to 10.31mm. What that actually means is that if you buy a 3/8 inch or 10 mm aquarium in the US, it may or may not work with your MP10. Ecotech give a maximum thickness of 9.5mm and if you buy an aquarium sold as 3/8 inch or 10mm glass it may be thicker than Ecotech's advertised limit for the MP10. This is why the Ecotech CS rep told the poster above that 8mm is the last common size that they guarantee to work. 8mm or 5/16" has an allowable range of thickness from 7.42 to 8.43mm to conform to US standards. Different countries have different allowable ranges of thickness. +1 for getting an MP40 to be sure.