[AdamHeard]

If I recall correctly, they have two threaded holes on the face for mounting.

As for a pinion, You can press a gear onto the shaft if it has the right bore size for a press fit. I think that would be just a few thousandths undersize, but I'm no expert in that. You can buy a gear with bore below that and open it up on a lathe, or you can turn a custom one from gear rod.

You could also buy a gear with a hub and set screw with a bore size the same as the shaft. Although set screws are not a good way to mechanically fasten the pinion to the shaft.

As for usage, I've only seen teams use them as a tachometer and I have to see a team power a system with them. I'm sure some have, I just haven't seen it. It's not terrible powerful, so there aren't many applications for it.