Other's more knowledgeable will verify or correct me, but I am pretty sure the 21 means 21 pitch. Not sure about the A or the 4 but I'd guess the 4 may stand for 4 blades....<br /><br />Anyone?
Westdevil,<br /><br />Could you be so kind as to at least let us know what kind of engine this prop is on?<br /><br />Alone the '21a4' could mean a lot or nothing.<br /><br />To help you getting the most out of this forum I'd like to point your attention to this good ol' post
