The Foredom® #15D Duplex Hammer Handpiece has the same specs as the Foredom® #15 Hammer Handpiece, except it includes a duplex spring for added flexibility. Foredom® #15D Hammer Handpiece has hammering rather than rotary action for use at low speed (0-5,000 rpm) by jewelers for stone setting and decorative work. Comes with an anvil point. It requires periodic lubrication. Hammer has 1/32" stroke and its impact can be adjusted from light to heavy by turning the silver knurled adjusting ring. 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 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" Foredom® #15 Hammer Handpiece is the preferable solution. 9 5/8" long. 1/4" diameter at tip. Instructions. Parts list.