Part of the F attachment linkage on King trombones. This is a black rectangular plastic connecting pivot rod with a pressed-in brass fitting. It is used as part of the string-action rotary valve linkages on King 607F, 608F, 3BF (2103F), 4BF (2104F) trombones, as well as older Bach B1102 and B1112 French horns. String and screws not included.