you can buy angle iron at most hardware stores.
the kind he's using has a 90 degree bend in it and
has holes all over it for passing bolts through.
Near as I can tell from his pics it looks like he used
another piece of similar material with all the holes in it but no angle,just flat. He mounted a piece of this to the top and bottom of his monitor. Then found a couple of places on the the top and bottom of the monitor where the holes line up with the angle iron , passed some bolts through and tightened it up.
slug54