Try \multicolumn<|l|> \tabularnewline in the relevant row. \multicolumn merges n cells with type q and places foo as content.
Side note: Using booktabs and vertical lines in a table is not the best design. I would also use left alignment for the first column.
\documentclass[11pt,a4paper] \usepackage[T1] \usepackage[utf8] \usepackage[english,italian] \usepackage \usepackage \usepackage[bindingoffset=1.5cm, left=3cm, right=3cm, top=3cm, bottom=3cm] \begin \title \author %\date \maketitle \begin \begin <|c|c|>\hline \multicolumn<|l|> \tabularnewline \hline Diametro fori (mm) & 4 \tabularnewline \hline Passo x (mm) & 24\tabularnewline \hline Passo y (mm) & 24\tabularnewline \hline Altezza canale (mm) & 10\tabularnewline \hline Lunghezza canale (mm) & 146\tabularnewline \hline Numero fori & 39\tabularnewline \hline \end \captionof \label \end \end
Since you're already loading the booktabs package, you should give serious thought to improving the overall "look" of the table by (a) getting rid of all vertical lines, (b) getting rid of most horizontal lines, and (c) using the macros \toprule , \midrule , and \bottomrule of the booktabs package for the remaining three horizontal lines. With these changes in place, figuring out how to get rid of the unwanted central vertical divider in the header row becomes unnecessary. Note that, in the table below, I also suggest not using c (centering) for both columns; instead, I recommend l (left-alignment) for the first column and r (right-alignment) for the second column.
\documentclass[11pt,a4paper] \usepackage[T1] \usepackage[utf8] \usepackage[english,italian] \usepackage \usepackage \usepackage[bindingoffset=1.5cm, margin=3cm] \begin \begin \begin lr @<>> \toprule Text \\ \midrule Diametro fori (mm) & 4\\ Passo x (mm) & 24\\ Passo y (mm) & 24\\ Altezza canale (mm) & 10\\ Lunghezza canale (mm) & 146\\ Numero fori & 39\\ \bottomrule \end \captionof \label \end \end
