%%
%% The LaTeX Companion, 2ed (second printing August 2004)
%%
%% Example 5-6-2 on page 266.
%%
%% Copyright (C) 2004 Frank Mittelbach, Michel Goossens,
%%    Johannes Braams, David Carlisle, and Chris Rowley
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3
%% of this license or (at your option) any later version.
%%
%% See http://www.latex-project.org/lppl.txt for details.
%%

\documentclass{ttctexa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{111.0pt}
\StartShownPreambleCommands
\usepackage{array}
\newcolumntype{I}{!{\vrule width 3pt}}
\newlength\savedwidth
\newcommand\whline{\noalign{\global\savedwidth\arrayrulewidth
                            \global\arrayrulewidth 3pt}%
                   \hline
                   \noalign{\global\arrayrulewidth\savedwidth}}
\StopShownPreambleCommands
\begin{document}
\begin{tabular}{|cIc|c|} \hline
 A  & B  & C  \\ \hline
 X  & Y  & Z  \\ \whline
100 & 10 & 1  \\ \hline \end{tabular}
\end{document}