setting style properties to table>tbody>tr>th cells

setting style properties to table>tbody>tr>th cells

hello!  trying to set the css class (or style properties) of th cells that are created with an asp.net gridview.  my html looks something like this:

<table>
   <tbody>
      <tr id="DT_V1_grdData_trueheader">
         <th>...
         <th>...
         <th>...
         <th>...
         <th>...
      </tr>
   ....


here are a couple of scripts i've tried to access the th cells w/in the first row, but neither of them work.  can anyone point me in the right direction? i feel like i've given up 1/2 a day on this...

            $("#DT_V1_grdData_trueheader").each(function() {
                $('th', this).each(function() {
                    $(this).addClass('hiddenHeader');
                });
            });


            $("#DT_V1_grdData_trueheader").find('td').each(function() {
                $(this).addClass('hiddenHeader');
            });