This is a proof of concept of a rotation lock that you can free with a push button.

You can print several arm.stl, parts and one bouton.stl part for each but one, and assemble them in one articulated arm.

If just trying it, you can cut the arm.stl part in two pieces in your slicer, and clip one in the other.

My goal was to design a simple to print and simple to assemble device. No screw required.

Just clip two parts with the button and a spring in between.

This design can be used to build adjustable feet for a bed tray for instance.