I bought a couple of these for a lego rc project and they have not dissapointed me. They stay on the motor very well and are sturdy enough for my purposes (little lego rc vehicle). Putting lego gearwheels w cross hole on the axle is easy, even though the fit is not perfect (getting them on requires a bit of force), but I see that as a positive point because it means the gears don't slip off. If I had to name a negative point it would be that they are quite long (axle is about the length of two standard beams and a gear + the length of the sleeve that goes on to the motor), but that may not be an issue depending on your build.