I bought a used MIM Strat neck a while back. There's a black plastic sleeve in the hole leading to the truss rod nut. The sleeve is tapered to follow the face of the headstock, like this one: When I adjusted the truss rod the sleeve spun with the bolt. When I used pliers in an attempt to spin the sleeve back or attempt to remove it, the pieces I grabbed snapped off. Is this a problem? Is that sleeve anything more than decorative?