I bought this for $5 a while ago. I have no idea what it is. The seller proudly proclaimed it was a very antique bookbinding tool. No, he didn't know I have an interest in bookbinding, so I wasn't baited. Too badly. Anyway, does have a bit of age on it, wood turned screws, etc. It is not very big, and hinged at the back. I think it's the back. It has been used a lot, the screws have worn corresponding holes in the board they push against. Of course, there are no markings. The only thing I can think of is it is used to trim small text blocks. One photo has a standard sized Zebra ink pen for scale. Anyone?
