\makeatletter
\def\TopRule{\noalign{\ifnum0=`}\fi
  \@aboverulesep=\abovetopsep
  \global\@belowrulesep=\z@
  \global\@thisruleclass=\@ne
  \@ifnextchar[{\@BTrule}{\@BTrule[\heavyrulewidth]}}
\def\MidRule{\noalign{\ifnum0=`}\fi
  \@aboverulesep=\z@
  \global\@belowrulesep=\z@
  \global\@thisruleclass=\@ne
  \@ifnextchar[{\@BTrule}{\@BTrule[\lightrulewidth]}}
\def\BottomRule{\noalign{\ifnum0=`}\fi
  \@aboverulesep=\z@
  \global\@belowrulesep=\belowbottomsep
  \global\@thisruleclass=\@ne
  \@ifnextchar[{\@BTrule}{\@BTrule[\heavyrulewidth]}}
\makeatother