From: rmowery42@charter.net   
      
   In article , peter@easthope.ca says...   
   >   
   > 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.   
   >   
   >   
   >   
      
   Same way that some connectors are left or right hand threads.   
      
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    * Origin: you cannot sedate... all the things you hate (1:229/2)