This is Version 3 of the plotter attachment. As in th3 version 2, 4 M3 screws are required. Two for holding pen and 2 for holding the attachment itself. Since the part is fully made up of plastic the Version 3 contains two holes for the M3 Nuts! and so this requires 2x M3 nuts.
However, I used only 1 hole which works fine as well.

Here is the link to the project:
https://www.patreon.com/posts/plotter-using-3d-24623711

Link to Version 2:https://www.thingiverse.com/thing:3380730/