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Cam-out happens when the driver bit climbs out of a screw’s recess instead of turning it. On square-drive screws, the first fix is usually a better-fitting, less-worn bit—not simply a more expensive one. A loose fit, excessive speed, a tilted driver, or a screw that has started crooked can all cause the same problem.
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Choose the right square-drive size
Square-drive screws are commonly sold in #1, #2, and #3 sizes. The bit should seat fully in the recess with little side-to-side movement. A #2 bit in a #2 screw is the usual match for general construction fasteners; larger structural screws may call for #3. Check the screw packaging when possible, because size and recess depth vary.
Do not force a close-but-loose fit. A bit that rocks in the recess concentrates force at the corners, where it can round the screw or chip the bit. If the bit will not seat fully, clear packed sawdust or debris before trying another size. Replace a bit with visibly rounded corners; an impact driver’s repeated blows will not make a worn bit fit better.
What bit to buy
For frequent driving with an impact driver, choose a purpose-made impact-rated square bit in the correct size. These typically use tougher steel and a torsion section intended to flex slightly under impact. That can reduce breakage compared with a standard hard, brittle bit, though it cannot correct a poor fit or prevent every failure.
For occasional assembly or a few screws, a basic quality square bit is often enough. Spending extra on a long bit set is hard to justify if you mostly use one screw size. Buy a short replacement bit in the size you use most, or a small set covering the sizes on your job. If you need to reach recessed fasteners, a longer bit helps access but gives you more leverage to tilt the driver and can wobble more.
Shop impact-rated square-drive bits when you drive these screws regularly. For occasional use, a small square-drive bit set is usually the more economical choice.
Compare the options
| Bit type | Best use | Trade-off |
|---|---|---|
| Impact-rated, short | Repeated screw driving with an impact driver | Costs more than a basic bit; less reach |
| Standard, short | Occasional fastening or a drill/driver | Can break sooner under heavy impact use |
| Impact-rated, long | Recessed or obstructed fasteners | More flex and wobble; easier to drive at an angle |
| Bit holder with insert bit | Changing bits often or reaching into a shallow recess | Adds another connection that can loosen or wobble |
Reduce cam-out while driving
Start the screw straight, and hold the driver in line with its axis. Press firmly enough to keep the bit seated, but do not lean so hard that you lose control or bend the workpiece. Begin at low speed or with gentle trigger pressure. Once the screw has started straight, increase speed as needed; slow down again as the head approaches the surface.
An impact driver’s hammering action is useful for driving long fasteners, but full trigger from the first rotation can make a screw skip before it has established a bite. Use a lower-speed setting if your tool has one. For delicate work, a drill/driver with a clutch can be easier to control than an impact driver. Set the clutch so it stops before the screw head damages the material, then adjust if it releases too early.
For hardwood, dense material, or large screws, drill a pilot hole when appropriate. Match the pilot-hole diameter to the screw and material rather than guessing; a hole that is too small raises driving force, while one that is too large weakens the screw’s grip. Avoid using an impact driver to compensate for a screw that is binding because of a bad pilot hole, a misaligned joint, or a screw that is too large.
Common failures and fixes
If the bit jumps out immediately, stop and check the drive size, seating depth, and alignment. If it begins well but slips near the end, reduce speed and pressure as the head seats. A screw head that is already rounded may not be recoverable with a fresh bit; continuing to hammer at it can make removal harder. Replace the screw when possible rather than repeatedly trying to drive it.
If bits break, first consider whether you are using a standard bit for sustained impact work, a long bit under heavy load, or a bit that is partly engaged. Use a shorter impact-rated bit where access allows and keep the driver square. If the screw stalls, back it out and check for an obstruction or an undersized pilot hole instead of holding the trigger against a stationary fastener.
A magnetic bit holder can make small screws easier to position, but it does not improve the fit between the square bit and screw. For consistent driving, use the correct bit directly in the driver when practical. Keep a spare of the size you use most: a fresh, well-fitting bit is often a better fix than a premium set.