This is a brake pump socket for all Silver Shadows, Wraiths, Corniches, Spirit/Spurs, Bentley T's,  Brooklands, Continentals, Eights, etc.  The factory tool on which this is based is part #RH8428.  If your Proper Motor Car has a brake pump, this is the socket for it.  This socket is made from heat treated Chromoly.  It has relatively thin walls in order to operate in tight spaces, so it is made from premium high-strength material.
British Tool Works also carries rebuild kits for SY/SZ pumps.  Look under the Parts tab.  We can also rebuild your pump for you starting at $225.00.  Contact us for details.