[Tuglist] vertical space of display equations 6pt accurately

[Baskaran]

Dear sirs,

Could we fix the above and below vertical space of display equations 6pt
accurately. 
I use the following commands but i can't get it.
\abovedisplayskip
\abovedisplayshortskip
\belowdisplayskip
\belowdisplayshortskip
\everydisplay
\baselineskip
\lineskiplimit
kindly request you that any other commands or penalty  to control the above
and below space fixed.

N.K. Baskaran