How to Use an Impact Driver (and Why Screws Strip)

Your manual wins. These are general practices. When your tool's manual says something different, follow the manual.

What an impact driver does

An impact driver spins like a drill, but when the screw resists it adds rapid rotational hammer blows. That's why it drives long screws and lag bolts with little wrist strain.

Use the right bits

• Impact drivers take 1/4-inch hex-shank bits only.
• Use impact-rated bits and sockets. Standard bits snap or round off under impact.
• Match the bit to the screw head exactly (PH2 for most Phillips deck screws, T25 for many Torx screws). A loose fit is the number one cause of stripped heads.

Speed modes

Many impact drivers have 3 or 4 speed modes, and some have a self-tapping or precision mode. | Job | Mode | | --- | --- | | Small screws, hinges, cabinet hardware | Lowest speed or precision mode | | Deck and framing screws | Medium to high | | Lag bolts, long structural screws | Highest | | Self-tapping metal screws | Self-tapping or low mode |

Technique

1. Seat the bit fully and push straight in line with the screw.
2. Start slow with a light trigger until the screw bites.
3. Keep firm forward pressure; most stripping happens when the bit climbs out of the head.
4. Stop the moment the head is flush. Impact drivers don't have a clutch, so it's easy to sink screws too deep.

When to grab something else

• Drilling clean holes: use a drill/driver.
• Concrete: use a hammer drill or rotary hammer.
• Precise, delicate screws: use a drill/driver with the clutch set low, or a screwdriver.