I acquired three of these several years ago, they were in a box of engravers and chip carver I purchased at a sale. Any idea what it is or how it's used. Looks like it would fit the socket of an anvil. Size; 6" long 3/8" at the short end 1/2" shoulder and tapers to 1/8"  hardened and has a manufactures mark. Direct  Link to photo as I'm having trouble with the attachment option.
http://i1214.photobucket.com/albums/cc496/camzim/Public/unkown2.jpg

Find the IMAGE tag and then click the img icon just above the text box- 

Then paste the img tag between the brackets.

I think it could fit into the hardy hole of an anvil, but tin smiths and silver smiths worked off of a steel plate set into a work table.   These had several holes for tools they could change out.   I have never seen a square tool bar such as this.   Tapered, so it could be for shaping, or straightening, you got me scratching my head. 

The smallest hardy hole I've seen is 1/2 inch.  Such a long, slender business end I can't see as surviving even the blows of a silver smith.  It looks to me like  the 3/8 end is meant to fit into a handle of some sort. 

If the edges were sharp, I'd call it a reamer... But they aren't. 

Can you get a magnification of the maker's mark?

Is the tip rounded or faceted?  It looks like a jeweler's broach to me, although I have not seen any that exact shape.  They were typically used in a jeweler's lathe to shape and enlargen holes.

Thats a ring guage for people with square fingers....... iWOULD SAY SOME SORT OF A MANDREL FOR SIZEING HOLES IN SOFT METALS 

Maybe jeweler's tool to form square settings for inlays.

I'd like to thank everyone for there help. Next thing I'll do is start searching appropriate catalogs. Unfortunately the makers mark is to small for a good photograph.

is the square/rectangle end anvil friendly?

Best closeup of makers mark I could get.
The square end has a slightly taper of about ten thousands.

Something under an imperial crown....why am I thinking silversmith mark?