I have created an universal / pen holder for the uArm Swift Pro. It is created in openScad, so you can easily modify if you like.
You can download the .stl and source code file here:https://www.thingiverse.com/thing:2345941
How do you attach it to the arm? One screw into the effector plate?
In the holder you can insert an M4 nut. (there is a cutout for this), then just slide in the universal holder (with the nut on top) and you can crew in the default M4 screw that also holds your suction end-effector.
Cool! What did you use it for? Why does the hole have this shape?
it is an universal holder but I use it to hold a pen, so that the uArm can draw.