This is a spring loaded pen module for the V1 Engineering lowrider2.
(Update: Added Lowerider2 Pen module variant 1.stl it uses Paper mate inkjot 550 RT pen and the end is pressure fit on no threading needed.)
Staples (postscript) pen.
Assembly take a m8x1 tap and make a thread in the bottom hole.
Disassemble the pen place spring on the top side of the pen ink stick see photo.
Insert pen ink stick & spring in module then screw the pen tip onto the module securely.
Make a tool step to 3mm and depth of 3mm