I've been designing a parametric model in Fusion 360 (view or download) that can be easily adjusted to different plant pots. The first iteration was quite a fail. I totally disregarded the fact that plant pots are circles (well at least the vast majority) so it ended up only fitting with one of its clamps.

Not exactly as intended...

It was also very bulky which I didn't like so I scrapped that clamp and designed a new one that was more compact. I stay with the initial concepts of having two halfs that are screwed together to clamp the rods in place.

This is how the new design looks like. It fits nicely on its intended pot. I gave about 0.3mm tolerance which I think weren't necessary, having a snug fit or even undersizing it a little might be beneficial.

I messed up the dimensions for the hex nuts, they were way too small. I ended up hot pressing them with a soldering iron which worked suprisingly well.

And this is how it looks on the pot (see below). I'm quite pleased with the result. It's compact but is still very strong.
The two bottom screws have two functions, first to give more strength in the case of lateral force where the plastic at the top screws might snap and second to deal with pots that have a weird shape where you may have a fat lip at the top or non linear curvatures.

In that case you can choose longer scews than needed (M3x12 countersunk) and screw them in deep enough to hit the pot to give extra support in these cases.

And here a "full assembly" with angle and light attached.