This is a used antique stitch marking iron, I think, (note the emphasis).  Overall length is 3.5" and the marking end makes a 1" wide pattern.  I used it to make several marks/impressions on thick cardboard, one of which I then partially touched up with a marker to emphasize the pattern it created.  Looks like an alternating stitch, doesn't it?  The tool was definitely hand fashioned, forged, cut and filed, likely by a blacksmith.  Unique, and one of a kind.