Hollow Bolt and Nut M12

This is an M12 screw and matching nut design with an extra feature, it has a cavity hole of 6.8mm.  The thread is 1.75mm pitch.  This can be used to pass 3D 1.75mm filament through it.

The cavity hole is sized to accept a small garden sprinkler tube, outside diameter of 6.75mm.  The sprinkler tube has an internal diameter of 4.00mm.  With heat, the sprinkler tube can be shaped.  I shaped the sprinkler tube to work as a 3D filament guide.  See photos.

The printed M12 screws and nuts needed a little attention to improve their screw threads.  You can simply use a metal M6 nut and bolt for this purpose; even better if you have an M6 tap and die to finish them off.

These 3D printed nuts and bolts should only be finger tightened.  Care!  Over tightening of the nut will sheer the screw from its head.

Here is my 3D design.  My design may match your needs, too.

My print is made in PETG 1.75mm Aurarum black filament, with 0.2mm layer height and 15% infill on a PRUSA I3 MK3S printer.

I hope you can find this design useful, too.