If I'm correct, it's part of a "James Walker" kit for making O-rings from strip material and Super Glue.
The O-ring cord would be put through the corresponding hole and a razor blade pushed through the slot to cut the cord square. The ends of the cord would then be joined using Super Glue.
I'm not sure how successful it was, but lining up the joint was hit and miss affair, although the vee grooves on the end of the tool were supposed to help with alignment. Plus, the joint line would be quite brittle.
Fine for emergency repairs I guess.