What is it - Flat blade holder in a box with machinists rules, trammel, etc.

I found this is a box of miscellaneous machinist tools. The other items in the box were rules and related accessories, part of a dial indicator holder, a trammel set, some protractors and some other small tools. It is about 8-1/2" long. The big end is about 7/8" wide and it tapers to about 9/16" wide. It consists on three 1/16" thick flat bars riveted together at the wide end. The middle bar sandwiched between the other two is only about 2-3/16" long, leaving a gap between the two longer parts. These two parts are bent slightly inward to make the gap spring closed at the narrow end. The very end of the narrow end has a couple of tapers maybe to facilitate pushing something flat in between the two sides so that it can be held by the spring pressure. The whole thing is made of stainless steel and has no markings on it.

Any ideas what it is, what it was used for or maybe what it is part of?