In article , ehsjr   
    wrote:   
   > The only difference I can see is the SH-12 is for nitrogen, the   
   > SH-16 is for air.   
      
   Understood.  One is marked "Air" and the other "N2".   
      
   A few microns or thousands of an inch can block interchangeability.   
   Obvious when fitting parts; not in photographs. Fitting a UNC nut to a   
   UNF screw is a more extreme example.   
      
   Thx,                    ... P.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)