\documentclass{article}

\usepackage{colortbl}
%\usepackage{booktabs}

\makeatletter
\def\hlinewd#1{%
\noalign{\ifnum0=`}\fi\hrule \@height #1 %
\futurelet\reserved@a\@xhline}
\makeatother

\begin{document}


\begin{tabular}{l l l}
\hlinewd{2pt}
\rowcolor[gray]{0.7}
First       & Second      & Third       \\ \hline
A A A A A A & B B B B B B & C C C C C C \\ \hline
D D D D D D & E E E E E E & F F F F F F \\
\hlinewd{2pt}
\end{tabular}

\vspace{1cm}

\begin{tabular}{|l |l| l|}
\hlinewd{2pt}
First       & Second      & Third       \\ \hline
A A A A A A & B B B B B B & C C C C C C \\ \hline
D D D D D D & E E E E E E & F F F F F F \\
\hlinewd{2pt}
\end{tabular}

\end{document}