Width in GridView

Hi,

I am trying to see if I could set the fixed width in GridView. This is what I use based on searching on Internet.

                    <asp:TemplateField HeaderText="Work Phone" SortExpression="WorkPhone" HeaderStyle-Width="20%">
                        <ItemTemplate>
                            <asp:Label ID="WorkPhone" runat="server" Text='<%#Eval("WorkPhone")%>' />
                        </ItemTemplate>
                    </asp:TemplateField>

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But it does not work. Am I missing something? thanks