Impact Driver Bits
Most impact driver frustration, from snapped tips to stripped screws to bits falling out, comes down to the bit. Here is what to use and why.
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Use impact-rated bits with a 1/4-inch hex shank. They have a torsion zone that flexes with each blow instead of snapping. Use 2-inch power bits or a magnetic holder with 1-inch insert bits. For most screws you only need Phillips #2, square #2 and Torx T25, plus a 5/16-inch nut driver for hex-head self-drillers. Match the bit to the screw exactly and replace worn bits early, because a worn tip is the main cause of stripped heads.
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What makes a bit impact-ready
An impact driver hits the bit thousands of times per minute. A standard screwdriver bit is hard and brittle, so those peaks crack its tip. Impact-rated bits survive in three ways:
- Torsion zone. A narrowed section of the shank twists slightly under each blow and springs back, like a shock absorber.
- Tougher steel and heat treatment. Steel that is slightly less hard but much less brittle, so the tip deforms rather than shatters.
- Precise tip geometry. Better fit in the screw recess means less cam-out, which is what actually strips screws.
You will see brand names for these designs: DeWalt FlexTorq, Milwaukee Shockwave, Makita Impact, Bosch Impact Tough, Wera Impaktor and others. All aim to do the same thing. Compare sets in the best impact driver bit sets, and see impact-rated vs regular bits for the detail.
Insert bits vs power bits
| Type | Length | Locks in collet? | Best for |
|---|---|---|---|
| Insert bits | ~1 in (25 mm) | No; use a bit holder | Cheap, compact sets; used with a magnetic holder |
| Power bits | 2 to 6 in | Yes (groove near shank end) | Most impact work; better reach and stability |
| Bit holder | 2 to 6 in | Yes | Holding insert bits; magnetic screw retention |
For most people, a few 2-inch power bits in your most-used sizes, plus a magnetic holder for the rest of your insert bits, is the ideal setup. See magnetic bit holders.
Drive types: which bit fits which screw
| Drive | Common sizes | Found on | Cam-out risk |
|---|---|---|---|
| Phillips (PH) | PH1, PH2, PH3 | Drywall, general wood screws, hardware | High |
| Pozidriv (PZ) | PZ1, PZ2, PZ3 | European screws and hardware | Medium |
| Square / Robertson (SQ) | SQ1, SQ2, SQ3 | Construction, cabinet and trim screws | Low |
| Torx / star (T) | T15, T20, T25, T30, T40 | Deck, structural and cabinet screws | Lowest |
| Hex nut driver | 1/4, 5/16, 3/8 in | Hex-head self-drilling screws | Low |
| Slotted | various | Older hardware | Very high; avoid with impacts |
Two mistakes cause most stripped screws: using a Phillips bit in a Pozidriv screw (they look similar), and using the wrong size, such as PH1 in a PH2 screw. Look at the screw box. It usually names the bit. Full charts are in impact driver bit sizes and Phillips vs square vs Torx.
The starter kit most people need
- PH2 power bits (several, since these wear fastest)
- T25 and T20 power bits for deck and structural screws
- SQ2 power bit for construction and cabinet screws
- 5/16-inch magnetic nut driver for hex-head self-drillers
- Magnetic bit holder for the odd sizes in your insert set
- A mixed impact-rated set to cover everything else
Impact-rated bit sets on Amazon PH2 power bit packs
Buy your most-used bits in bulk packs
A big mixed set looks like value, but most people wear out one or two sizes and never touch the rest. Buy PH2 and your deck-screw Torx size in multi-packs, and keep one good mixed set for everything else.
Beyond screwdriver bits
- Hex-shank drill bits: pilot holes and small holes in wood and metal.
- Spade and auger bits: fast holes through framing.
- Socket adapters and hex-shank sockets for nuts, bolts and lags.
- Right-angle attachments for tight spaces. Make sure they are impact-rated.
Making bits last
- Push firmly and keep the bit in line with the screw. Angle causes cam-out.
- Use the right speed. Full speed on small screws strips them and wears tips. See speed settings.
- Stop when the screw seats. Hammering on a seated screw just chews the recess.
- Replace bits early. A rounded tip costs more in ruined screws than a new bit costs.
More fixes in how to stop stripping screws.
Safety: non-impact bits can shatter under impact. Wear eye protection, especially when driving into metal or using bits of unknown quality. See impact driver safety.
Frequently asked questions
Can I use regular bits in an impact driver?
They fit if they have a 1/4-inch hex shank, but they wear and snap much faster under impact, and brittle bits can shatter. Impact-rated bits cost a little more and last far longer.
What does impact-rated mean?
The bit is designed to survive repeated hammer blows, usually with tougher steel and a narrowed torsion zone that twists slightly and springs back, absorbing peak forces that would crack a standard bit.
Why do my bits keep falling out of the impact driver?
Short 1-inch insert bits have no groove for the collet to grip. Use them in a bit holder, or use 2-inch power bits with a groove near the end of the shank. A worn collet can also lose grip.
Which bit do deck screws use?
Most modern deck screws use a Torx/star drive, commonly T20 or T25. Some use square drive. Check the screw box, because the right bit is usually listed and often included.
How long do impact bits last?
It depends on the screws and technique. Replace a bit as soon as the tip looks rounded or starts to cam out. Running a worn bit damages screw heads and wastes time.