It saves space for boomstand placement on your rack tubes, to just put them on the top of a horizontal pole.
That's done with this clamp bracket.
It will save you a clamp (or 2) on your rack tube, that are also a more expensive solution than this bracket.
Especially when you want to stay within the Gibraltar shiny ecosystem.
No modification necessary, just need to remove a end cap, put this over the top and use the drum key to tighten.
Works fine.
It's not build for on and off installation because the tightening screws will leave marks on the tube, so it's better to make this a permanent modification.
There are some brands here and there offering this kind of bracket, but this one has all the necessary tube size inserts included.
Except, in my case, if you buy a complete Gibraltar rack assembly (not from Thomann) and it turns out Gibraltar kept the spare inserts for themselves when they put the assembly in the box.
That is typical Gibraltar sloppyness...and arrogance.
But well, they do make some good stuff.