Sliding angle grinder stand

Did I miss something? At 28:50, he press fits the square tube of the slide into the U shaped supports. There does not seem to be anything other than the friction of the pint to hold it into place. I looked at the beginning and it is the same.

I like the basic concept. I have some 8"x8" beams to clean up the ends on which were flame cut and I could build something that clamps to the beam to run the angle grinder to clean up the edge. Won't work on the web, but that isn't as important to me.

Sliding angle grinder stand - video