to Jit different -sized Nuts or Heads of Screws. 451 



composing the block machinery in this dock-yard* and I 

 have always considered it as an object of great importance, 

 for the preservation and neat appearance of engines, to at- 

 tend to all the means which would obtain these advantages, 

 and such, 1 think, will arise from the use of my universal 

 wrench. 



It is, perhaps, unnecessary to point out, that a wrench 

 on this principle mav be varied in its form and size, so as to 

 be rendered probably more convenient for some particular 

 purposes for which such instruments are required. 



I am, sir, your obedient servant, 



Portsmouth Dock Yard, Wm. BARLOW. 



March 1, 1808. 



To C. Taylor, M.D. Sec. 



Reference to the Engraving of Mr, Barlow's Improved 

 Wrench. See Plate XIII. Figs. 5, 6, and 7. 



This instrument is represented in Plate XIII. Fig. 5 is a 

 perspective view of it ; fig. 6 a section of its head ; and fig. 

 7 an external representation of the head. The screw head 

 or nut to be turned is held between twt> jaws, one of which 

 a b d e is forged in the same piece with the handle A A, the 

 other, f g, is moveab'e between two chukes, and fastened to 

 the fixed jaw by the strong screw i, which is fixed to the 

 same jaw, passes through the moveable one, as shown in 

 the section fig. 6, and has a nut screwed upon it ; the other 

 screw, h, is tapped through the moveable jaw, and its point 

 presses upon the bottom of a cavity made in the fixed jaw 

 shown at m in the section fig. 6. To make the wrench fit 

 any particular screw head or nut, the nut upon the strong 

 screw i must first be loosened, and the screw h screwed in 

 or out of the moveable jaw, until the opening hg is just 

 the proper width to receive the screw head or nut to be 

 turned by the wrench j the nut of the screw i is then to be 

 screwed down, until it presses upon the jaw, and holds it 

 perfectly tight. 



Ffs LXXXI. On 



