3-pin metal jumper is one of two different jumpers that are used on the original 73355 Heater Relay Board. On the new style Heater Relay Board there are two of this 3 pin jumper. The jumpers are inserted flat just above the gray terminal block numbered 1-5. The 2-pin jumper is also used depending on the spa model and whether it's wired 120v. or 240v.