If you use a hockey puck, I wouldn't recommend the blue ones.
At the sports store near me, there are two kinds of pucks labelled "marking" (black) and "non-marking" (blue).
I was happy with the black ones. They're easy on the tire and they last a long time. But I tried a blue one to see if it would last longer. It blew up after about a mile.
After I cut out the rubber "donut" with hole saws, I epoxy it to a steel spacer. The spacer goes over the motor shaft and is held with set screws. It sounded like the blue roller started slipping just before it broke. Maybe a different glue (like urethane) is needed for the blue ones, but I'll just stick with plain old black pucks and epoxy.
In the pic, you can see how the puck has been screwed to a block of wood for drilling. I get two rollers from a puck. There is the broken blue roller and a black one that I haven't attached to that spacer yet (still have to drill and tap that spacer). Then I'll have one on my bike and two spares.