This rhythm circuit has a bassier, neck-pickup only range. Another new feature was a spring-loaded rubber string mute, which was flipped upwards from under the strings by a lever. The mute was designed for guitarists who had to palm mute for extended periods, which was difficult or impossible on the Jaguar's floating bridge without knocking the bridge out of position. This feature proved unpopular and became known as a "tone killer"; the cover and its foam were usually quickly removed. The bridge on many versions of the Jaguar has become known for several design shortcomings and consequent problems. The "threaded" bridge saddles allow the strings to slip out of alignment if they are plucked or strummed hard, motivating some players to fit replacement saddles that have deeper slots or grooves to hold the strings, or to replace the bridge completely. The Fender Mustang style bridge is a popular choice of replacement. Another issue sometimes encountered is a tendency for the bridge's support posts to slip down into the holes that house them. Players have found various solutions to this issue, including wrapping tape around the bridge posts. Like the Jazzmaster and Bass VI, the Jaguar has an unusual floating vibrato mechanism that was a complete departure from the "synchronized vibrato" system found on the Stratocaster. Leo Fender believed that this new design was superior to previous designs since the bridge actually moved backwards and forwards along with the strings during vibrato use, thereby maintaining proper intonation even under duress, and preventing strings from binding. This floating bridge concept was also later used on the Fender Mustang. The floating vibrato mechanism also features a built-in lock, which helped the player preserve the guitar's tuning in the event of a string breakage and easing removal of the vibrato arm. Variations Fender 50th Anniversary Jaguar To celebrate the 50th anniversary of the Jaguar in 2012, Fender released a USA-made model that featured a C-shaped maple neck with lacquer finish and vintage-style truss rod, bound 9.5"-radius rosewood fingerboard with 22 medium jumbo frets and pearloid block inlays, a modified one-degree neck-angle-pocket cut to improve pitch, a re-positioned tremolo plate to increase bridge break angle to prevent string slippage and increased sustain, a custom neckplate and specially designed hotter wound single-coil neck and bridge pickups for fatter tone and more output. The 50th Anniversary Jaguar was available in three Custom Colors: Burgundy Mist Metallic, Candy