I ordered this by mistake as my shield is 'thin series'. But this thick one fits, no problem. In fact, if you have a "thin series" with enough extra space, I recommend thick series breakers for your 2 pole breakers. They occupy 4 slots in the thin series panel, but the pin connections create a larger contact area, resulting in less thermal distortion over time. (which is important on these old panels). I had to move something and cut out another panel overlay, but everything works fine. And all my fears of replacing the entire panel are now gone. Great smooth breaker. On a thin serial panel, however, you won't be able to replace all thin switches with thick ones. You would end up running out of space. But it's a good idea to replace 2 poles. Air conditioning, stove and dryer. In any case, the danger comes from the old 2-pole switches and not from single-pole ones for lighting and sockets. THIS IS NOT ADVICE, JUST MY OPINION. CONSULT AN ELECTRICIAN IF YOU ARE NOT AN ELECTRICIAN. WORKING ON ELECTRICAL PANELS IS DANGEROUS. IF YOU ARE NOT PROPERLY PREPARED, YOU MAY RECEIVE AN ELECTRIC SHOCK.