NGK-ZFR6F-11 ..... what does the 11 mean?

[CasopoliS]

I called NAPA today to see if they could order me NGK-ZFR6F. Rich (505zoom) is running these and likes them... so I figured I would try them.
NAPA says they can get me NGK-ZFR7F or NGK-ZFR6F-11
Just wondering why the 11..... anyone know what this is referring to? I plan to gap .030
Other plug suggestions are ok too (thumb).
Thanks in advance.

 

[A.V.MSP]

Im pretty sure it has to do with the gap

 

[CasopoliS]

This is from NGK's site:

 

[uclap5]

its the gap in mm.