SDS drills are rotary hammer drills with a chuck system that allows the drill bit to move up and down independently for extra power during drill hammering. SDS chucks work with a variety of bits for drilling, hammering and chiseling.
"SDS" stands for "special direct system," which describes the unique chuck mechanism of an SDS drill. Bits push into the mechanism and are held in place by a tight spring. The shape of the shank of the bit keeps it from slipping during rotary drilling. During hammer drilling, the bit is powered directly by the drill, moving easily in and out of the chuck. This provides added power for hammer drilling on concrete and masonry. According to Popular Mechanics, SDS drills are not suited for most normal do-it-yourself projects. An all-purpose drill is a better choice, and SDS drills are available at power tool rental facilities for heavy-duty jobs.