Pair of nylon thimble sleeves for stabilizing bridge rocking on Jazzmaster/Jaguar guitars when using tremolo. These keep the bridge centered and allow slight flex for improved tuning stability. Fender now puts thimble sleeves in some higher end American models. These US-made sleeves aren't a Fender part (7710508000) but have similar diameters and are slightly longer for even better stability. Easy/reversible installation: insert them into the stock bridge thimbles, then place bridge posts into the nylon sleeves.
These work with most American Jaguar/Jazzmasters, Mexican and Classic Vibe models, and others with vintage American Specs. Photo shows sleeves installed in a Classic Vibe 40th Anniversary Jazzmaster.