Spoke nipple clamp © 2023 by Tristan Thomas is licensed under CC BY-NC-SA 4.0 
https://creativecommons.org/licenses/by-nc-sa/4.0/?ref=chooser-v1

Bolt:
M3 cap screw.  You can go as short as 12mm but I find a 14mm or 16mm is better because it gives your fingers something to grip and you're less likely to drop the bolt.

Brass insert:
M3 thread with 4mm OD.  Any length up to 8mm 

Square nut:
Nominal 5.5 x 1.8mm (the standard size that is included with Prusa printers) 

You can change the nut dimensions and clearance in Fusion's parameters. 

I suggest you press the square nuts while the print is still warm 