\begin{center}
    \begin{tikzpicture}
        \draw[step = 0.5cm, gray, very thin] (-7.25, -1.25) grid (7.25, 0.25);

        \node[mill, /mill = hammer] (A) at (-4.5, -0.5) {};
        \node[anchor = south] at (-4.5, 0.25) {\textbf{hammer}};

        \node[mill, /mill = impact] (A) at (-1.5, -0.5) {};
        \node[anchor = south] at (-1.5, 0.25) {\textbf{impact}};

        \node[mill, /mill = vibration] (A) at (1.5, -0.5) {};
        \node[anchor = south] at (1.5, 0.25) {\textbf{vibration}};

        \node[mill, /mill = roller] (A) at (4.5, -0.5) {};
        \node[anchor = south] at (4.5, 0.25) {\textbf{roller}};
    \end{tikzpicture}
\end{center}