How to set the width of the cells in the same GridView column?

I have a gridview that is filled with some data. I need that the cells of a column have all a fixed width.

The code I have is the following but it does not work, since the cell is much smaller.

<asp:BoundField DataField="Descuento" HeaderText="Descuento" SortExpression="Descuento" ><ItemStyle Width="74px" Wrap="true" /></asp:BoundField>