Impact Driver Glossary
Spec sheets, reviews and tool boxes are full of shorthand: IPM, Ah, torsion zone, cam-out, 20V Max. This glossary explains each term in plain English, with links to deeper guides where they exist.
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This is a plain-English list of impact driver terms, from amp-hours and anvils to torsion zones and XPT. Each entry is one or two sentences, sorted alphabetically, with a link to a full guide where one exists. The terms that matter most when buying are torque, IPM, RPM, brushless, Ah and impact-rated. Use the section headings to jump to a letter.
On this page
How to use this impact driver glossary
Terms are grouped alphabetically. Every term has an anchor, so you can link straight to it. If you are starting from zero, read what is an impact driver first, then use this page as a reference. A few numbers come up so often that they are worth having in one place:
| Unit or label | Meaning | Quick reference |
|---|---|---|
| in-lbs | Inch-pounds of torque | 12 in-lbs = 1 ft-lb |
| ft-lbs | Foot-pounds of torque | 2,000 in-lbs = about 167 ft-lbs |
| RPM | Revolutions per minute (no load) | How fast the bit spins |
| IPM / BPM | Impacts or blows per minute | How often the hammer strikes |
| Ah | Amp-hours of battery capacity | Higher means longer runtime |
| 1/4-inch hex | Standard impact driver bit shank | Fits every mainstream impact driver |
A-B: Amp-hour to Brushless
- Amp-hour (Ah)
- A measure of battery capacity. A 4.0 Ah pack runs roughly twice as long as a 2.0 Ah pack of the same voltage, and is larger and heavier.
- Anvil
- The part of the impact mechanism that the hammer strikes. It is connected to the output shaft and passes each blow to the bit.
- Assist mode
- A mode on some drivers (Makita and Ryobi, for example) that starts slowly to help a screw bite, then speeds up once impacting begins.
- Auto-stop (reverse auto-stop)
- An electronic feature that stops the tool shortly after a fastener breaks loose in reverse, so nuts and screws do not fly off.
- Bare tool
- A tool sold without battery or charger, often with a "-20", "B" or "Z" suffix. Good value if you already own the platform.
- Bit
- The interchangeable tip that engages the screw head. Impact drivers take 1/4-inch hex-shank bits. See impact driver bits.
- Bit holder
- An extension that holds short insert bits, often magnetic, adding reach and quick changes.
- Brushed motor
- An older motor design that uses carbon brushes to switch current. Cheaper but less efficient, and the brushes wear out.
- Brushless motor
- A motor switched electronically instead of with brushes. More efficient, cooler-running and longer-lived. See brushless vs brushed.
C-H: Cam-out to Hydraulic
- Cam-out
- When the bit rides up and out of the screw recess under torque, chewing the head. Common with Phillips screws, worn bits and angled pressure.
- Clutch
- The adjustable torque-limiting collar on a drill/driver. Impact drivers do not have one; they use speed modes instead.
- Collet (quick-release chuck)
- The spring-loaded 1/4-inch hex socket on the nose that locks bits in. Read about types in impact driver chucks and hex collets.
- Drill/driver
- A standard cordless drill with a clutch. It drills holes and drives screws with smooth rotation, without impacts.
- FUEL
- Milwaukee's name for its top-tier brushless tools, combining its POWERSTATE motor, REDLINK PLUS electronics and REDLITHIUM batteries.
- Hammer
- The spring-loaded rotating weight inside an impact driver that disengages and strikes the anvil when the fastener resists.
- Hex shank
- The six-sided end of a bit that fits the collet. Impact drivers use 1/4-inch hex; round shanks do not fit.
- Hydraulic driver (oil-pulse, oil-impulse, pulse driver)
- An impact driver that delivers its blows through a sealed oil chamber instead of steel on steel. Much quieter, with lower torque. See hydraulic impact drivers.
I-P: Impact driver to Power bit
- Impact driver
- A compact cordless tool with a 1/4-inch hex collet that adds rotational hammer blows when a fastener resists, driving long screws with little wrist strain.
- Impact-rated
- Bits, sockets and adapters made from tougher steel to survive impact loads. Standard bits can chip or shatter. See impact-rated vs regular bits.
- Impact wrench
- A bigger relative of the impact driver with a square drive (3/8, 1/2 inch and up) for sockets, bolts and lug nuts.
- IPM (impacts per minute)
- How many hammer strikes per minute the tool delivers at full speed while impacting. Explained with RPM in IPM vs RPM.
- Kit
- A tool sold with one or more batteries, a charger and usually a bag or case. Often a "-22" or "K" suffix.
- Lag bolt (lag screw)
- A heavy wood screw with a hex head, driven with a socket adapter. Usually needs a pilot hole.
- Max voltage (20V Max, 12V Max)
- The battery's peak voltage with no load. A 20V Max pack is about 18V nominal, the same class as 18V tools.
- Mode (drive control)
- A preset speed and impact setting selected with a button. Low modes protect small screws; high modes drive big fasteners. More in speed settings and modes.
- Nominal voltage
- The average voltage a battery delivers under typical use. Five lithium-ion cells give about 18V nominal.
- Pilot hole
- A smaller hole drilled first so a screw or lag drives straight, without splitting wood or stalling the tool.
- Power bit
- A bit 2 inches or longer with a groove near the shank end that locks directly into the impact driver's collet.
R-S: Robertson to Stall
- Robertson (square drive)
- A screw recess with a square socket. It grips well and resists cam-out; common on deck and construction screws.
- RPM (revolutions per minute)
- How fast the output spins with no load. Many drivers list a separate maximum RPM for each speed mode.
- Runout
- Wobble at the bit tip caused by play in the collet or a bent bit. Impact drivers have more than drills, which affects precision.
- Self-tapping screw mode
- A mode that drives self-drilling metal screws at high speed, then slows as the screw seats to avoid stripping. Milwaukee's 2953 includes one.
- Socket adapter
- A hex-to-square adapter (usually 1/4 or 3/8 inch) that lets an impact driver turn sockets. Use impact-rated versions.
- Stall
- When the fastener stops turning even though the tool is impacting. A sign the fastener is too big, the pilot too small or the pack too weak.
- Star Protection
- Makita's battery-to-tool communication that guards against overload, over-discharge and overheating.
T-X: T-mode to XPT
- T-mode
- Makita's mode for self-drilling (Tek) screws: it drives fast, then cuts speed when the screw seats to prevent overtightening.
- Torque
- Rotational force, rated in in-lbs for impact drivers. Brands measure it differently, so cross-brand comparisons are rough. See torque explained.
- Torsion zone
- A thinner, slightly flexible section of an impact-rated bit that twists a little to absorb peak loads and prevent breakage.
- Torx (star drive)
- A six-lobed screw recess that transmits torque well with very little cam-out. Common on structural and deck screws.
- Variable-speed trigger
- The trigger controls speed by how far you squeeze it. Feathering it is the main way to control small screws.
- Wobble
- Loose bit movement in the collet. Some play is normal; excessive wobble points to a worn collet or a damaged bit.
- XPT
- Makita's Extreme Protection Technology, which improves dust and water resistance on certain tools.
Terms that are often confused
- Impact driver vs impact wrench: hex collet for bits vs square drive for sockets.
- Impact driver vs hammer drill: rotational blows for driving vs forward blows for drilling masonry.
- 18V vs 20V Max: the same five-cell battery, labeled by nominal or peak voltage.
- RPM vs IPM: spin speed vs hammer strikes per minute.
- Insert bit vs power bit: short bit needing a holder vs longer bit with a locking groove.
Impact-rated bit sets on Amazon
Frequently asked questions
What does IPM mean on an impact driver?
Impacts per minute: how many times the internal hammer strikes the anvil each minute at full speed while the tool is impacting. It is listed alongside RPM, which describes how fast the bit spins. Higher IPM generally means faster driving under load.
What is the difference between in-lbs and ft-lbs?
Both measure torque. Twelve inch-pounds equal one foot-pound. Impact drivers are usually rated in inch-pounds and impact wrenches in foot-pounds, so 2,000 in-lbs is about 167 ft-lbs.
What does the M in 20V Max stand for?
Max refers to the maximum voltage of a fully charged battery measured with no load. A 20V Max pack has the same five cells as an 18V pack, which is about 18 volts nominal under use.
What is the difference between an insert bit and a power bit?
Insert bits are short, usually 1 inch, and sit in a bit holder. Power bits are longer, 2 inches and up, and have a groove near the end of the shank that locks directly into an impact driver's quick-release collet.