Not dovetail, but could be a router jig for box joint joinery. All heavy steel, again likely from some high volume production box/ crate woodshop.
Joe B
Works on evenly spaced half blind dovetails and for through dovetails also. The only caveat is that the pin socket and distance between the pins be equal. 1/2" pins spaced on 1" centers, for example. You get pin taper from the bit. For through dovetails the pin side board would have to be pretty thin, <= 1/2" from the looks of those.
One of the first woodworking tools I bought was a router, shortly after that I bought a dovetail jig. It has fixed plates similar to those. Mine has rounded ends on the tabs though, enables you to cut perfect fitting blind dovetails with a countoured end that matches the space formed by the bit when at the back of the jigs slot. Easy way to make wood drawers and trays. Once set up you can consistently cut both pins and tails in less than a minute. (You cut pins and rails at the same time, if you are cutting evenly spaced dovetails. The boards are jigged offset by one space.)
Chilly
