VMarten created a nozzle holder that uses M6 nuts.
I didn't have any, so I got built this.
8 by 8 matrix of holes marked:
0.2 0.3 0.4 0.4 0.5 0.6 0.8 1.0
My printer doesn't print an M6 nut thread correctly, so I made a Calibration holder that prints a range of diameters for the holes.
Print that and determine the smallest diameter size your nozzles will fit, then choose the next one up.
The hole diameters are embossed on the calibration holder.
Print that STL.
Where I got the idea:
3D Solutech PLA
YMMV (or your printer), which is why it has the calibration object.
I used a large wall size to make is solid.