The bearings are press fit into the roller and use the M5 screws as axles.
The author remixed this model.
I modified these models to use a 625Z bearing, commonly used for rollers on many 3D printers.
Additional required parts:
Two 625Z bearings (16mm x 5 x 5)
Two M5 x 12 Button head screws (can be longer)
Two M3 x 25 mounting bolts