This model was originally created by @GJ FLA from the FutureProofHomes.net Discord server….all credit to them for the original design.  

The support posts on the original were designed to have M3 fasteners screwed directly into the plastic.  For this model, I've slightly enlarged the the posts so that they work with ruthex M3 threaded inserts.  

The diameter of each hole is 4MM, and the cylinder of material that surrounds each hole is 1.75MM thick (which is slightly greater than ruthex's min thickness of 1.6MM for the M3 inserts).  The holes are 15MM deep on the long posts, 10MM deep on the shorter posts (I've used M3x8 screws for the long posts and M3x12 screws for the short posts). 

I did not need to use XY hole compensation when printing in PETG-HF on my X1C.  The final printed hole diameters was about 3.8MM…but since the threaded inserts were melted into place, this was not an issue. 

note: with @GL FLA's permission, I've included his original design files.