The spring connects the two separated ends of a handpiece and is all that distinguishes these handpieces from standard models. The duplex spring component requires periodic lubrication. Duplex Springs provide extra flexibility to a handpiece when more precise control for delicate work is required. The spring drive is made of special steel, double wound, tubular construction with a protective flexible spring cover. Replacement springs can be installed by the user. Duplex springs are subject to breakage and are NOT covered by warranty.