You are bidding on a Morrison Model C Loud Speaker Unit, or horn driver, made in the 1920’s.  It is in nice clean condition with good nickel plating.  It is good, clicking and measuring about 2150 ohms with my meter.  It has a tone adjustment on the back, which varies the pressure on the diaphragm.  It is identical to the drivers used in De Forest Sets with internal horns, like the D-12 and D-17, except that it is not labelled De Forest.  A previous owner has added a new cord.  I've never seen one of these previously that was not frozen, and could not be opened, so this is a nice one!  It measures roughly 2 3/8 inches in diameter and is 1 1/2 inches deep, not counting the neck or adjustment control.  The neck is 3/8 inches long with an outside diameter of 7/8 inches, and inside diameter of almost 3/4 inches.  It should be great for your project.  Shipping weight is 1.25 pounds. Please see my other auctions for more radio and audio items, and tubes.