Thanks for the compliments, I appreciate them.
Regarding the HDZ, yeah, that’s not too surprising. I have one of the Mr. Beaver first run HDZ units. Also, here are the fasteners I bought to use for the brackets and drag chain.
The bracket above has oversized holes to use an aluminum spacer, washer and screw combo to allow you to hold the 3D printed part securely and clamp the end plate to the rail securely - but without crushing the 3D printed part.
The aluminum spacer is sized to allow you to tighten the button head screw tight enough to keep the end plate from moving, but protect the 3D printed part from crushing completely. The aluminum spacer is 0.0625" shorter than the 3D printed bracket thickness, so the 3D printed part can be compressed up to that thickness before the spacer takes the force.
The washer will distribute the load from the button head screw to the 3D printed part, and it is thick enough it will not deform (much) and hold the 3D printed part securely.
For the four long fasteners that hold the drag chain into the brackets, I did not actually put nuts on the bottom side of them. It turns out that they stay in place just fine, and it is easy to just pull them out if needed for whatever reason - like feeding more crap into the drag chain.
I am trying to remember what countersunk fasteners I used, I think they were just some stainless steel hex socket ones, also from McMaster-Carr. I’ll go out to my shed and see what I can see regarding them.
For the fasteners that hold two 3D printed parts together, I just printed the parts with three perimeters and six top/bottom layers, and tapped the plastic and screwed them in directly. They are NOT coming out, so putting in brass threaded inserts is just not needed.
EDIT: Yup a bunch of 4-40, 6-32 and 8-32 screws.