I have no knobs on my B620 but I have two nuts welded on where I could place a few bolts. I actualy wondered what they were for until now.
My Rops were rattling upright so I put 3 layers of electrical Rubber tape on the arms and pushed them back up and pinned to stop the rattle.
It will wear out but has worked so far. Next I will go for small pieces of intertube.
This was just my fix on a new piece of equipment.
Actually, One rops mid bracket is weleded off center from the other one. It has kind of a tilt to it like it wasn't leveled when welded.
But since you all say the rattledit probably wouldn't make a differnce how it was welded.
Tom