This is a jumper pin that can be used for both the ECLER NUO2 and NUO2.0 mixers. The NUO2 and NUO2.0 are famous for their high sound quality, but the output level is set low at the factory. By installing this jumper pin, you can get a +6dB effect, further enhancing the sound quality. Although this information is originally included in the instruction manual, it is also explained in detail on the Shimamura Music website, so it may be helpful to refer to it. Basically, anyone can easily install it by opening the cover with a Phillips screwdriver and inserting this jumper pin into the dedicated terminals. This listing is for 5 jumper pins in total: 4 for use and 1 spare (the mixer itself is not included).