.10D has the same specs as the H.10, except includes a duplex spring for added flexibility. H.10D is a slender handpiece with rotating lever action that releases and closes the collet for quick and easy changes. It requires lubrication after the first 2-3 months of continuous use. For use ONLY with 2.35mm (3/32") burs. Duplex springs are subject to breakage and are NOT covered by warranty.They are made of special steel, double wound tubular construction with a protective flexible spring cover. Replacement springs (HP76) are available and can be installed by the user. We recommend that only experienced users of flex shaft tools consider purchasing this style handpiece. For most users, the "straight" handpiece (H.10) is the preferable solution. 10-3/4" long, 21/32" dia.