I don't think that I've ever seen them talked about on here. What are everyone's thoughts about them? I've got a buddy who's rebuilding his pump, and is planning on buying one. Are they worth it, and do they really do what they're supposed to? At what speed and horsepower are they needed, if at all? He also said that he found one that doesn't need any machining of the impeller shaft, it slides on and uses 1 or more setscrews to hold it in place. But I haven't been able to find this one, and I'm not to sure if I like the sound of it just being held in place by setscrews because of the forces being applied to it at higher RPMs. Thanks.