SK 42 extrusion heatsink. From Fischer Elektronik, the SK 42 standard extrusion heatsink is made from anodised aluminium in a grilled shape. Extruded heatsinks are the most common form of heatsink and are suitable for a range of medium power applications. The SK42 Heatsink is available in the following lengths:. Stock number ; 189-8599 189-8599 is 100mm long. Stock number ; 189-8606 189-8606 is 150mm long. Stock number ; 189-8612 189-8612 is 200mm long. Stock number ; 189-8628 189-8628 is 75mm long.