How to make double lines to only one bold (thick) line

Question

How to make the double lines to only one bold (thick) line ?

\documentclass[french]{beamer}
\usepackage{babel}
\usepackage{adjustbox}
\usepackage{array}
\newcolumntype{C}[1]{>{\centering\arraybackslash}p{#1}}
\begin{document}   

\begingroup
\defbeamertemplate{enumerate item}{image}{\small\includegraphics[height=1.8ex]{images/gofor}}
\makeatletter
\def\@listii{\leftmargin\leftmarginii
              \topsep    2ex
              \parsep    0\p@   \@plus\p@
              \itemsep   \parsep}
\makeatother
\begin{frame}{Conclusion}
\begin{table}
\centering
\caption{Comparatif entre ATL et MFC}
\vspace{0.4cm}
\begin{tabular}{
  | C{0.07\textwidth}
  *{3}{|C{\dimexpr0.22\textwidth-2\tabcolsep\relax}}
  ||C{\dimexpr0.22\textwidth-2\tabcolsep\relax} |
  }
\hline
& {\fontsize{9}{9}\selectfont Gestion avancée des threads} & {\fontsize{9}{9}\selectfont Gestion de la mémoire} & {\fontsize{9}{9}\selectfont Vitesse d'exécution} & {\fontsize{9}{9}\selectfont Difficulté} \\
\hline
MFC & \adjustbox{valign=c}{\includegraphics[height=1.8ex]{example-image-a}} & \adjustbox{valign=c}{\includegraphics[height=1.8ex]{example-image-a}} & \adjustbox{valign=c}{\includegraphics[height=1.8ex]{example-image-a}} & \textcolor{green}{F}\\
\hline
ATL & \adjustbox{valign=c}{\includegraphics[height=1.8ex]{example-image-a}} &\adjustbox{valign=c}{\includegraphics[height=1.8ex]{example-image-a}\includegraphics[height=1.8ex]{example-image-a}} & \adjustbox{valign=c}{\includegraphics[height=1.8ex]{example-image-a}\includegraphics[height=1.8ex]{example-image-a}\includegraphics[height=1.8ex]{example-image-a}} & \textcolor{red}{D} \\
\hline
\end{tabular}
\end{table}
\end{frame}
\endgroup
\end{document}

Answer 1

Two vertical rules separated by a space (of \tabcolsep in tabular) is given by || in the column specification. To remove the space between them, use |@{}|. If you want it thicker, you can use |@{}|@{}|, or add more @{}|'s.

\documentclass{beamer}
\begin{document}   

\begin{frame}
  \begin{tabular}{c | c || c |@{}| c |@{}|@{}| c |@{}|@{}|@{}| c |@{}|@{}|@{}|@{}| c}
    A & B & C & D & E & F & G
  \end{tabular}
\end{frame}

\end{document}

Answer 2

I would recommend not using vertical rules, so the problem of thicker rules vanishes. But here's how you can do it.

\documentclass{beamer}
\usepackage{array}

\newcolumntype{I}{% I for a thick rule
 !{\vline width 1pt}%
}
\newcolumntype{J}[1]{% variable thickness rule
 !{\vline width #1}%
}
\begin{document}

\begin{frame}
  \begin{tabular}{c | c || c I c J{2pt} c J{3pt} c }
    A & B & C & D & E & F
  \end{tabular}
\end{frame}

\end{document}

The specifier I gives a rule 1pt thick; change 1pt to suit your needs. With J you specify a thickness.