I don't pretend to understand much of this but precision aluminium profile (and box? it is extruded) apparently conforms to DIN 17615:

DIN 17615
Outer Dimensions: Depending on size, 0.2 to 0.4 mm
Straightness Deviation: Max. 1.5mm/2m
Flatness Deviation: Max. 1.5mm/2m

http://www.maytec.org/technische_daten_e.htm
and
http://www.drivesystemsgroup.com/PDF...ue%20(DSG).pdf

also this is an interesting read, or would be if it wasn't so late
http://www.easy-conveyors.fi/materiaali/NTS_GB2002.pdf