Is it really a 1/2" router bit?

I bought my first 1/2" router bit at that woodworking shop going out of
business.
It is an adjustable slot cutter.

Well, it is 1/2" at the base, but 1/4" where the interchangable cutters and
bearings go. Is this really a 1/2" bit, or is it a 1/4" bit with a 1/2"
base? Or am I making distinctions that don't matter?

I guess the good part of it is that I can put my 1/4" rail and stile
components on it...