" 

 Metric or imperial? 
 Most datasheets of SSOP devices I see describe the lead-spacing (pitch) to be 0.65 mm (aprox 0.026""). For example: http://www.national.com/ds/LM/LM4866.pdf (page 20). Though other national semiconductor SSOP items seem to use 0.025"" (0.635 mm): http://www.national.com/packaging/folders/mqa16.html 
 The difference becomes large quickly: 20*(0.65-0.635) =0.3mm, about half the pitch! 
 I don't know what is correct, but I'd say it should be mentioned?   "