Being as it is a balanced item, it is probably meant to run at a fairly high RPM; the four holes equal distance from the center bore look to be for some sort of flange attachment, but that is speculation on my part. My first thought was that it was for use in a PTO application, as it is "military packed", but again, speculation. Looking at the tag that you picture, I see the first line says it is a "Lo" Gear, and the .409 might be the bore diameter?? The fourth line says NSF Mech. P(ump)(?). So, I speculate that it is a drive gear for some sort of high speed, high pressure pump. Purely conjecture on my part, but I couldn't resist opining on your question. The real possibilities are almost endless.