Milwaukee 3048-20 M12 FUEL impact wrench

Impact rate, in impacts per minute (IPM), counts how often the hammer mechanism strikes the anvil when the tool is under load. More impacts per minute generally helps fasteners seat faster, but it works together with torque and speed, so do not judge a tool on this figure alone.

The anvil is the square drive that holds sockets, commonly 3/8, 1/2 or 3/4 inch. Retention type matters: a hog ring (friction ring) allows quick socket changes, while a detent pin locks sockets in more securely. Use impact-rated sockets that match the anvil size.

Tool-only weight is the bare tool without a battery, as listed by the maker. Add the battery weight to estimate what you will actually hold, since larger packs add noticeably. Weight matters most for overhead, ladder and all-day work. Makers do not always measure weight the same way.

Tool length is the front-to-back measurement published by the maker. A shorter tool fits between studs, joists and inside cabinets more easily; standard US framing is 16 inches on center, leaving about 14-1/2 inches between studs. Check whether the figure includes the chuck or bit holder.

Brushless motors use electronic control instead of carbon brushes, which generally means less wear, less heat and more runtime per charge. Brushed motors are simpler and often cheaper, and are fine for lighter or occasional use, though their brushes can wear out over time.

This lists how many batteries come in the box, if any. Tool-only (bare) listings include no battery or charger, which suits buyers already on that battery platform. Two batteries let you charge one while working with the other.

Amp-hours (Ah) is the battery's charge capacity. At the same voltage, a higher Ah pack runs longer between charges but is usually larger and heavier. Smaller packs keep the tool lighter for overhead and light work; larger packs suit saws, grinders and other high-draw tools.

This states whether a charger is included and which type. Chargers vary in output, so the same battery can take noticeably different times to charge on different chargers. Tool-only listings usually include no charger.

This is the maker's published warranty term. Terms for tools, batteries and chargers often differ, and some depend on registration or exclude certain uses. Read the maker's terms for what is covered, how claims are handled and whether proof of purchase is required.