I bought a deer lure feeder to spread scratch grains to my chickens. It has tube legs, which will end up filling with dirt. I could cap them, but I thought it would be nice if they had feet that auto-leveled. I could have stopped at the plug with a ball on the end, but I added a ball-joint foot, too. It should work for angles up to 27 degrees.

The model has the individual parts and the assembly. I recommend splitting or deleting the assembly, as the ball insert is a floating model and may fail the print if the socket tolerance is too large. The ball, oriented with the insert side down, shouldn't need supports. Once printed, press the ball into the socket. It will snap in with a little effort, but with no tools needed, and rotate pretty freely.

The model is freely adaptable with variables for the insert (different tube sizes), ball joints, and foot base sizes. I also provided variables for the socket tolerance and clearance percentage (the sizing down of the opening the ball pushes into). To have those variables, you'll need to go to OnShape, where you can export the model or, with a free OnShape account, copy and update those variables or any other dimension of the parts to your heart's content.