Hello,
From an older topic I know that the internal radii seems to vary between 3.6 and 3.8mm.  The outer radii varies between 4.8 and 5.2mm.  That has been measured by hand. Is this information still true today (any process improvement?). 
What about the tolerance of the 20 mm of the side of the tube ? Is it +/- 0.1 mm ? In my application the tube shall slide inside the groove of roller which looks like this one <https://www.aliexpress.com/item/10-56-31mm-belt-groove-H-type-injection-molding-machine-safety-door-roller-square-groove-D10/32816622292.html>. The groove profile shall fit the tube side profile as close as possible. 

We have not sourced any different specification box sections, so the existing tolerances have remained the same.

From a structural perspective, okemont is right in that you need to take care in terms of loading up these in a structure due to the construction  of the tube and the limiting factors that can effect pultruded  section.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant