Drill, Hammer Drill, Rotary Hammer, Impact Driver: The Four-Tool Taxonomy
The four common rotary power tools look similar but solve different problems: a regular drill for general holes and small screws, a hammer drill for the occasional brick hole, a rotary hammer for concrete and masonry, and an impact driver for driving screws. Names are misleading because hammer drills barely hammer and rotary hammers are really hammers that happen to rotate.
Four power tools dominate the rotary-tool category, and the names actively confuse buyers. Knowing which one to reach for matters because each is built around a different internal mechanism and excels at a narrow task. A regular drill or driver uses planetary gear reduction with a torque clutch. It handles general holes in wood, steel, and plastic plus small-to-medium screws. It cannot meaningfully drill concrete, and large augur bit work overwhelms its low-speed power. A hammer drill (sometimes sold as a combination drill) adds a crude ratcheting cam of bumpy metal faces rubbing together, producing a tiny reciprocating tickle. It works on brick and struggles through small concrete holes, but it is the wrong tool for any serious concrete work. The hammering hardware adds permanent weight and failure points in exchange for occasional utility. A rotary hammer is the actual concrete tool. It uses a swash plate bearing to drive a free-floating piston in a sealed cylinder, producing real percussive force. Any concrete hole larger than about 6 mm wants a rotary hammer. It typically lacks a real gearbox, so it makes a poor general-purpose driver. Rotary hammers usually take SDS chuck bits rather than round-shank bits. An impact driver is the secret weapon. It has no clutch, no shifting gearbox, and no reciprocating piston, just a spring-loaded mass that stores energy when resistance rises and releases it in rotational hammering bursts. It drives screws of any size and handles general drilling in wood and steel, though it is unusually loud and demands hearing protection. The practical buying advice: if you own only one tool, get a regular drill with a clutch. Add a hammer drill only if you want occasional brick capability. Buy a rotary hammer the moment you face any real concrete work. Add an impact driver if you install a lot of screws. The best two-tool kit for most people is a regular drill plus an impact driver. See also Drill Clutches: Mechanical Ball-and-Spring Versus Electronic Current Sensing, Rotary Hammer Pneumatic Mechanism: Free-Floating Piston Driven by a Swash Plate, Impact Driver Mechanism: Spring-Loaded Hammering Without a Clutch.