This is an antique Thayer combination hammer (or compound hammer as Thayer called it). It has a small tack pull on one end of the shank or bar and a screwdriver on the other end. The shank  is graduated to form a scale or ruler.  Adjacent to the tack pull there is a bulge in the hammer head to act as a fulcrum for the tack pull. The hammer head along the shank is adjustable. The shank  fully opens to 9.5 inches. The wooden handle has a rich aged patina and 2 brass ferrules, one at each end of the handle. On one side of the 
hammer 's metal shank or frame is hallmarked THAYER'S PAT(ENT), JUNE 24,1862. This lovely hammer has been in my collection for years. It is now looking for a new, loving home. It is a good example of 19th century tool invention and innovation and is published in the book: The Remarkable Hammer. p.148. The tool comes with a photocopy of the patent.

Length: 9.5 inches
Width: 3.5 inches