I agree that it is a box scraper, designed to clean up the inside corner of a lidded box. I added this post only to mention that I do a lot of threading of small turned boxes and use one of these, reground to NRS, to "sneak up" on the ID of the workpiece that receives the inside threads. Because it's sharp and handy, I also use it for final surface conditioning of any surface near where the threads will be/have been cut, either ID or OD.