Mystery bevel gear part? Radar?

[atreyu]

I was given this a while ago and I've recently cleaned it up. It's stamped O-521-PB-B75. My first hunch was something off a radar system? It's either had a wiper or large dial attached to the splines.

 

[MiTasol]

It could also be part of a trim tab control, many were about that size and had the handle attached to the splines