# Why does my table have cropped corners?

I was trying to use the tabular environment and noticed something strange so I increased the line width and then it became obvious that the corners of the table are cropped.

This would be the code:

\documentclass{book}

\usepackage[utf8]{inputenc}

\setlength{\arrayrulewidth}{1mm}
\setlength{\tabcolsep}{18pt}
\renewcommand{\arraystretch}{1.5}

\begin{document}
\begin{center}
\begin{tabular}{ |c|c|c| }
\hline
1 & 2 & 3 \\
\hline
\end{tabular}
\end{center}
\end{document}


And this would be the output:

• That's expected. – egreg Jun 29 '17 at 22:09
• @egreg Do you mean this "feature" is intended by design, or do you just mean that you knew already it was so ? – marsupilam Jun 29 '17 at 22:15

The "strange" corners are fixed by package array, see section "2.1 Handling of rules".

\documentclass{book}

\usepackage[utf8]{inputenc}

\usepackage{array}
\setlength{\arrayrulewidth}{1mm}
\setlength{\tabcolsep}{18pt}
\renewcommand{\arraystretch}{1.5}

\begin{document}
\begin{center}
\begin{tabular}{ |c|c|c| }
\hline
1 & 2 & 3 \\
\hline
\end{tabular}
\end{center}
\end{document}