This is an interesting workbench that is located at a PA historical site

To see the full size picture, just click on it.

This has some unsual construction features.  The top is made of three 4" thick boards.
The board in the back is 16" wide, the next one is 6" wide and the one in the front is 4" wide.
 Length is close to 8 foot.  The board jack slides on a board with a tongue on top with the
groove in the jack itself.  The board is dovetailed into the front of the legs.

 
 The dog row is pretty unique.  The dogs are wooden blocks, 2" square, fitted tightly into the front
board.   You just tap them up or down with a mallet.  No springs that I could see
holding then and evern after all the years this bench has been around they still are pretty snug.

 
 Another interesting feature is that the tail vice front jaws have iron plates screwed into the ends.  The
main vice also is fitted with iron plates as well.

  
 
  The back jaw of the tail vice doesn't have an iron plate.
 

 
The main vice as noted before, also has iron plates, but they only extend down to the top
of the rails.  The bench top itself is tapped for the vice screw.  As you can see, the rails
sit a little bit above the screw, so that any work being held in there wouldn't contact or damage
the screw threads.  Who ever made this bench (and there was no indication of the
provenence of the bench) sure knew what he was doing!