A genuine Fender part for locking this guitar into a fixed bridge instead of a floating vibrato. Sold generically for Mustang guitars rather than this specific model, so worth confirming fit before buying.
Why we say this
This is the genuine Fender part matching the hardtail stoptail conversion this guitar's own description flags as an available upgrade path. It is sold generically as a Mustang part without specifying which generation of Mustang mounting it matches, and this guitar's own Dynamic Vibrato has a confirmed generational difference from older Mustang vibratos, so the same caution reasonably applies here without independent confirmation.