LaTeX Tables – varying line width
\hline is not your only option.
One of the easiest ways to vary the line width in your tables is with the booktabs package, which provides lines (or rules) of predefined width. The lines \toprule, \midrule, and \bottomrule are great to use for a table. Each rule can also be specified, locally or globally, for your own weighting preferences.
Table using hline:
\begin{document}
\begin{tabular}{ccc}
\hline
1 & 2 & 3 \\
\hline
4 & 5 & 6 \\
\hline
7 & 8 & 9 \\
\hline
\end{tabular}
\end{document}
Output:
Table using booktabs:
usepackage{booktabs}
\begin{document}
\begin{tabular}{ccc}
\toprule
1 & 2 & 3 \\
\midrule
4 & 5 & 6 \\
\midrule
7 & 8 & 9 \\
\bottomrule
\end{tabular}
\end{document}
Output: