Nickel. Tremolo for thin acoustic-electric guitars (like Bigsby B7). Spring and mounting screws are included. The Duesenberg Radiator Tremolo canreplace an original Bigsby B7 because the mounting holes have the sameposition. The tremolo also features a "strings-through-roller bar" mounting (fast and easy string changing). So you have no trouble with the ball ends, which have to be put over the pins and for which you actually need a third arm when changing strings (Bigsby users know what I mean).