GT2 16 Teeth 6,35mm (1/4") Timing Pully (6mm width).
It is designed to being milled with CNC.
This model contains a dual option to lock the pully in place.
There are 2 holes for a set screw "DIN 913 - M2,5 x 4" or "DIN 913 - M2,5 x 5"
Teeth dimensions are taken from the web and should be accurate for 2mm pitch belt.
DXF file available for easier dial in on your CNC.
For the Idler https://www.thingiverse.com/thing:2620411
For the smooth idler https://www.thingiverse.com/thing:2620438
Although this is designed for CNC, it can be 3D printed.
Keep in mind, if you print this you will need to cut the thread of 2.5mm by hand in the model as it has no other option to guide the set screw.
It is better to use this https://www.thingiverse.com/thing:2618634 for printing, or any other pulley available on Thingiverse