Chosen Solution
Looking for the washer that is on the left device and missing on the right device. The device is a Sony Mic Transmitter UTX-B2 but I could not find the washer by searching its name online.
@teaouu that “washer” is actually a nut. Take it to a good hardware store and see if they can match it up. This will most likely be a metric thread. Otherwise, any good electronic repair or machine shop can most certainly help you out. what you are looking for is the nut (arrow) that holds the stereo mini-jack (4) in place. Sony part number for that is 1-507-743-21 and is really hard to find. Just get a nut from another 3.5mm audio jack.
