Power handling in resistors depends on the overall appearance of the component. The flange has to be flat with no scratches, otherwise air pockets with very high thermal resistance will form. This could lead to failures in the field due to hot spots. Bourns uses high quality copper in its flanges for this reason. The thickness of the flange leads itself to less pliability and better coplanarity, so Bourns offers a unique 6 mm flange thickness.