Fischer elektronik 21 heatsinks for to 220221 housing fischer elektronik fk 237 sa 220v the fischer elektronik 21 attachable heatsink has been specially developed for to 220221 and features a narrow clip on heatsink for vertical installation with additional solder tabs for fixing the components to a pcb fischer elektronik fk 237 sa 220v 21cw heat sink for to 220 housing