I've been given several propellers, and can't claim to be all that familiar was props in general. The lot is comprised mainly, if not completely, of Mercury props. One has no part # on it, but is a 3 bladed prop that is surrounded/contained in a round shroud. It's a factory build prop, all aluminum, ends of each prop is perfectly welded to the outer round shroud. Can anyone provide info as to the name of this style of prop is and what it's designed application may be? Thanks in advance.