The metal bar on the rear of the CVC4 is its heat spreader. Most LED dimmers don’t attach any form of heatsink or spreaders to their MOSFETS. We have added a one for the CVC4 to spread the heat generated by these components over a wider surface area to promote passive cooling, smooth out any sudden temperature rises and to give a longer lifespan. (In the previous 73925 CVC4 design, the MOSFETS were bonded directly to the aluminium case).