[RobotDoktor]

Retain things? Zip-ties of course! ... just kidding.

In a gearbox I usually see bearings on the ends and spacers in between gears when appropriate. For more spaced out options hex collars are good as long as the load isn't too large. We have had he collars slip on our drivetrain due to the forces when strafing. Fortunately the distance was not very far, so there wasn't a problem.