Rule thickness in pixels.
<HR size=2> - the default and smallest
<HR size=6>
<HR size=10>
<HR size=20 noshade> NOSHADE causes the browser to draw the line as a plain black line without the three dimensional shading.
Rule width can be expressed as a percentage of the screen or the exact width in pixels.
<HR width=100%>
<HR width=50% align=left>
<HR width=25% align=right>
<HR width=400> width in pixels