I'm pretty sure I've solved the tool mystery. Looking for something else, I happened across an old catalogue of printer's supplies.
I can't post a picture but this link should lead to an image of the right page:
http://www.archive.org/stream/convenientbookof00allirich#page/n16/mode/1up
Have a look at the bottom left - the lead cutters. I think it's one of those.
(Btw 'leads' were long thin pieces of type metal used to space lines of type the right distance apart. They would have been fairly soft but tough enough to need a well-made tool to cut them.)
I can't post a picture but this link should lead to an image of the right page:
http://www.archive.org/stream/convenientbookof00allirich#page/n16/mode/1up
Have a look at the bottom left - the lead cutters. I think it's one of those.
(Btw 'leads' were long thin pieces of type metal used to space lines of type the right distance apart. They would have been fairly soft but tough enough to need a well-made tool to cut them.)