I hadn’t done the complete math to see what would be needed. Just ruffing it out using US measurements and materials, the conduit’s inside dimensions of .75 inches, or roughly 19mm would allow a maximum of a .53 inch square or 13.43mm. Again, I’m only looking at materials available in the US, but I’m sure metric sized material would also be available that could work for the 25mm conduit. Half inch angle iron may be a workable fit. It’s commonly.125 thick with a slight radius on the edges. I’ll have to pick up a piece and give it a try.