ORIGINAL: DeviousDave
IIRC, the glow props (which the 4.2-4 is) don't use shaft bushings, just the electric. I don't see a ring inserted in the prop in the pic, but the resolution isn't good enough to say. I've bought only a few 4.2-4's since they were available and I don't think I have ever known them or the other 1/2A props to use pressed in bushings like the electric props do.
That's exactly how I understand it too - the props with bushings are electric, those without are 1/2A. It;s all on their site.
MJD