There's now a v2 version of this model. I very much recommend to use the new version. It has some general improvements with alignment and the new version includes .step files for easier customization. You can find it here:
https://www.printables.com/model/1302508-neptune-3-proplusmax-voron-afterburner-carriage-v2
More infos on my N3P Mods: https://www.reddit.com/r/ElegooNeptune3/comments/1e35xoj/upgraded_neptune_3_pro_showcase/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button
The carriage and the other parts use M3 x 5mm(w) x 4mm(l) threaded inserts.
The author remixed this model.