We now have a shaft we can mount a bearing to and hold the bearing in place. Without any custom machining. But what holds the bearing? This does..
This is a bracket with a bearing placed in it.
Here are two brackets capturing a bearing..
You then can hold the brackets with a stationary bracket..
But there's another type of bracket that is useful...
The axle bracket.
This bracket has the 8mm D-profile cut into the middle. This bracket can either hold a shaft stationary to your assembly. Or it can engage a shaft that is made to rotate smoothly by riding in a set of bearings..
Such as here in my trebuchet model.
But either of these brackets can be used for yet another purpose. Given any gear or pulley. If you can center it up properly and drill your holes right. You can bolt any gear or pulley or sprocket to one of these brackets.
The possibilities are endless.