I only found one reference, but it matched my guess...
Cylinder ridge reamer.
(On a moving piston the rings stop a bit below the top of the cylinder in an engine, wearing it larger everywhere but at the top. The reamer cuts that undersized area away so the entire cylinder is the same size when rebuilding an engine.)
That one looks a little different than the classic style, I suspect it has an alignment piece to keep it true.
PS: The design looks very much like Zim's