H.15D has the same specs as the H.15, except includes a duplex spring for added flexibility. H.15 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. We recommend that only experienced users of flex shaft tools consider purchasing this style handpiece. For most users, the "straight" handpiece (H.15) is the preferable solution. 9-5/8" long, 1/4" dia. at tip, wt: 5.2 oz.