Around the Switchcraft speaker outlets for "auto" impedance switching. Just an affectation? If there to keep out grime , it does not work, and intermittent contacts with almost every one I see. So each time I see one I clean the contacts and fit a small nylon cable tie through the tip contacts bunch and around / through the wiring to the other pins and draw tight enough to retain a circular form and add pressure to the closing contact but not so tight its not possible to plug into or extract a plug.