M30x100 Bolt with Nut

An M30x100 bolt and the nut that goes on it.

The nut is an exact fit and is very sensitive to printer calibration (filament diameter, extrusion steps, etc.); you may need to scale it up 1-3% or so to get it to go onto the bolt smoothly. A nut scaled up by 5% will still screw on fine but will be a little bit loose.