Graph Tech ResoMax NV2 Auto Lock Bridge with String Saver Saddles 4MM Posts Gold Proprietary, lightweight ResoMax alloy increases harmonics in every noteString Saver saddles eliminate string breakage, super lubricating and corrosion resistantAutoLock magnetically locks the bridge and tailpiece in place without any tools to use or loseTriple plated chrome, 24K gold, nickel, black and black nickel finishes for years of durabilityMade for 4mm post diameters