This is a handle and insert to hold a standard utility razor blade for use in chamfering sharp wood edges.  There are 2 different size slots - one for 1/16" and one for 1/8".  

CAUTION: this tool is designed for use with extremely sharp razor blades.  Please exercise caution when working with sharp objects.  Wear gloves or use a wood block when inserting the razor blade and holder.

Printing note - depending on your printer tolerance, the insert may need to be scaled down slightly to fit better.