The is a 19th century hand-forged iron quilting clamp, with one of this sort often referred to as a "heart clamp" for the heart shaped finial on the screw. It would have been used for clamping the fabric layers of a quilt (top, batting, backing) to the rails of a frame while working it (sparing the quiltmaking from laborious pinning, etc.)
Once a month I go up to midcoast Maine for a show, and once a month, for a few months now, I bring home an old iron heart quilting clamp or two! I've purchased them all from the same good dealer at an antique shop I stop at, and all come from the same old tool collection I am quite sure--the dealer has just chosen to set them out one or two at a time. Last weekend I returned to the scene, and two new ones had been put out since last I visited, both of which I scooped up promptly: I love them as objects--and valentines!-- and they're quite rare in my experience to find. And what a heart on this one, its lobes like mickey mouse ears! This one is a bit larger and heavier than the other listed today, and is the first of its form I've found (these were typically made in sets of four; the other I've listed today is the fourth, and I presume final, of a set I've been picking up one by one, selling as I do, not knowing that its mates would emerge!
5" t x2 1/2" with screw closed; screw itself 4" long. Very nice antique condition, nice patina to the iron, screw turns smoothly.