1010 aluminium buying guide

Hi, it’s the first time I’m buying aluminium extrusion. And I want to build the gridbot 2.5. In the BOM I found 1010 450mm aluminium extrusion. Is it referring to 1010 metric or imperial? If it’s imperial would a 2020 metric extrusion (20mmx20mmx450mm) be sufficient? Does it matter if it’s t or v slotted. Considering I buy the correct nuts for it?

yes, 20mmx20mm is what’s expected for the build