Why the vocabulary matters
Power tool packaging is dense with abbreviations and ratings. Some describe how the tool is built, some describe how it performs, and some are safety markings. Knowing which is which makes it easier to compare tools fairly and to follow the manual. The definitions below are grouped by theme. Exact numbers and symbols vary by manufacturer and region, so treat the manual for your specific tool as the final word.
Electrical terms
Volt (V). The electrical “pressure” a tool is designed for. Corded tools in North America typically run on household current, often listed as 120 V. Cordless tools list the battery voltage instead.
Amp (A). The amount of electrical current a tool draws. On a corded tool, the amp rating on the label tells you roughly how hard the motor can work and how much load it places on a circuit. It is useful context for understanding tool amperage and for avoiding an overloaded outlet.
Watt (W). Volts multiplied by amps. Some tools list watts as a rough measure of power input, which is not the same as the power delivered at the chuck or blade.
Amp-hour (Ah). A battery capacity rating. A higher number generally means more stored energy and longer run time between charges, though weight and cost also rise.
Brushed and brushless motors. Brushed motors use small carbon contacts to deliver current to the spinning part of the motor. Brushless designs use electronics instead. Brushless motors often run cooler and can be more efficient, which is why brushless motors appear on many newer cordless tools.
Double insulated. A construction approach that lets a tool operate safely with a two-prong plug and no grounding wire. It is usually marked with a symbol of one square inside another.
GFCI. Ground-fault circuit interrupter, a device in an outlet or plug that cuts power quickly when it detects current leaking where it should not.
Battery platform. A manufacturer’s family of tools that share one battery type. Choosing a battery platform means choosing which batteries and chargers you will keep using across tools.
Speed and force terms
RPM. Revolutions per minute, how fast a chuck, blade or bit spins.
No-load speed. The speed the tool reaches when nothing is cutting or driving. Under load the speed drops, so the box number is a maximum.
Torque. Twisting force, usually listed in inch-pounds or foot-pounds (or newton-meters). It is separate from speed. A tool can spin fast with little twisting force, or slowly with a lot.
BPM and IPM. Blows per minute or impacts per minute. These describe how many times a hammering or impacting mechanism strikes each minute. They show up on hammer drills and on an impact driver.
SPM. Strokes per minute, the back-and-forth rate for jigsaws and reciprocating saws.
Stroke length. How far the blade travels in one back-and-forth motion.
Variable speed. A trigger or dial that lets you change speed. Good variable speed control helps you start holes without skating and match speed to material.
Clutch. An adjustable mechanism on drills and drivers that slips at a chosen torque to protect screws and material.
Soft start. A feature that ramps up motor speed gradually so the tool does not jerk on start-up.
Holding and cutting terms
Chuck. The clamp at the front of a drill that holds the bit. Types include keyed, keyless and SDS.
Collet. A sleeve that grips a round shank, common on routers and rotary tools. Collets come in specific sizes, and using the wrong size is a safety problem.
Arbor. The shaft that a blade or wheel mounts on, also the name for the hole size in the center of a saw blade. A blade must match the arbor size of the saw.
Shank. The part of a bit or accessory that goes into the tool.
Kerf. The width of material a blade removes as it cuts. It is why a cut board ends up slightly shorter than the sum of its pieces.
Tooth count and TPI. The number of teeth on a blade, or teeth per inch on a hand or jigsaw blade. More teeth typically give a smoother but slower cut, while fewer teeth cut faster and rougher. Different saw blade types suit different jobs.
Bevel and miter. A bevel is an angle across the thickness of the board, and a miter is an angle across the face or width. Many saws can set both.
Depth of cut. The maximum thickness a blade, bit or cutter can reach in one pass.
Runout. Wobble of a spinning part away from a true circle, which can cause rough cuts and extra wear.
Tearout. Splintered or ripped wood fibers around a cut, often at the exit side.
Pressure and air terms
PSI. Pounds per square inch, a measure of air pressure.
CFM. Cubic feet per minute, a measure of airflow volume. Air tools list how much air they need and compressors list how much they can supply.
Duty cycle. The share of time a tool or compressor is intended to run versus rest.
Hammering terms
Hammer drilling. A mode that adds rapid forward blows to the rotation, meant for masonry. The basics of hammer drilling masonry belong with the tool types designed for it, such as a rotary hammer, which uses a stronger striking mechanism than most drills.
SDS. A bit-holding system with slots that let the bit slide back and forth for hammering action, as opposed to a gripped round shank.
Safety markings
Most tools carry warnings about eye protection, hearing protection and dust. A few common ideas:
- Read the manual before use. Usually shown with a book icon.
- Wear eye and ear protection. Shown with glasses and ear-muff icons.
- Unplug or remove the battery before changing accessories. One of the most common instructions, and one of the most important when unplugging tools before any adjustment.
- Rating marks from testing labs. These show that a sample was tested to a published standard. They are not a guarantee of safe use.
Reading a spec sheet
Compare like with like. Two tools may list different units, such as amps on one and watts on another, or maximum speed on one and speed under load on the other. When a number looks impressive, check what it measures. Ratings tell you about a tool’s capability, but build quality, balance and accessories often matter just as much in daily use.
Terms that sound similar
A few pairs cause regular confusion:
- Speed versus torque. Speed is how fast something turns. Torque is how hard it twists. A high RPM figure says nothing about how well a tool drives a large screw.
- Volts versus amp-hours. Voltage describes the pack’s design level, while amp-hours describe how much energy it stores. A higher-voltage pack is not automatically longer-lasting.
- Bare tool versus kit. A bare tool is sold without battery or charger, while a kit includes them. Check what is in the box before comparing prices.
- Capacity versus recommended use. A maximum capacity, such as the largest bit size or material thickness, is a limit and not a target. Working near the limit usually stresses the tool.