Phillips vs Square vs Torx

The recess in the screw head decides how much torque reaches the screw before the bit slips. With an impact driver, that choice matters more than most people think.

Updated October 10, 20266 min readBy the ImpactDriver.net team

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Torx vs Phillips vs square: the short version

All three drive types work, but they handle torque very differently. Phillips tapers, so torque pushes the bit out of the screw. Square drive grips well and holds the screw on the bit. Torx has the best torque transfer of the three and the lowest cam-out. With an impact driver, which delivers high torque in sharp blows, those differences decide how many screws you strip.

Why Phillips screws cam out

A Phillips recess is a cross with sloped walls. When you apply torque, those slopes create an upward push on the bit. Once that push beats the pressure from your arm, the bit rides up and out. That is cam-out. With an impact driver, every blow is a torque spike, so each one tries to lift the bit. Do it a few times and the bit rounds the recess.

The fix is not to stop using Phillips screws, since drywall screws and most hardware use them. It is to use the right size, push hard and run a lower speed. Full technique is in how to stop stripping screws, and if you already rounded one, see how to remove a stripped screw.

Square drive: grip and screw retention

The square, or Robertson, recess has straight walls with a slight taper. The bit wedges into the recess, so a screw stays on the tip without a magnet. That makes square drive great for one-handed starts, overhead work and screws in awkward spots. Cam-out is low because the walls are nearly vertical.

Square drive is common on construction screws, cabinet and face-frame screws, trim screws and many combo-drive deck screws. Its weakness: at very high torque, the square corners can round over, especially with a worn bit. Square bits also come in sizes that look similar, so an SQ1 in an SQ2 screw slips immediately.

Torx: best torque transfer for impact drivers

Torx, often sold as star drive or six-lobe, uses a six-point star with rounded lobes and near-vertical drive walls. The bit pushes sideways against the walls, not up and out. That means almost no cam-out, much higher torque before damage and longer bit life. It is why nearly every modern deck screw, structural wood screw and many cabinet screws use it.

With an impact driver, Torx is the most forgiving drive. You still need the right size and a straight line, but you can drive long screws without fighting the bit. Weaknesses are small: Torx sizes are close together, so a T20 can fit loosely in a T25 recess and then strip it, and cheap off-brand star screws sometimes have shallow recesses.

Common sizes for each drive

Sizes depend on the screw gauge and the maker. The full chart, from #6 to #14 screws, is in impact driver bit sizes. The box usually names the bit, and deck and structural screw boxes often include one.

Which drive to choose by job

When you buy screws, you choose the drive. For anything you will drive in bulk with an impact driver, choose Torx. The deck-specific method is in how to drive deck screws, drywall in hanging drywall with an impact driver.

Other drives you will run into

• Hex head. Self-drilling metal screws, some structural screws and lag screws use an external hex head driven with a nut driver or socket. These take high torque well, since the driver grips the outside of the head. A 5/16-inch magnetic nut driver covers most self-drillers.
• Slotted. Old hardware and some electrical terminals. A slotted bit slips sideways and out with almost any torque, so avoid it in an impact driver and use a hand screwdriver.
• Combo drive. Many construction screws accept both Phillips and square bits. Use the square bit for better grip.
• Security and specialty drives. Tamper-proof Torx with a center pin, spanner and tri-wing need their own bits. They show up on appliances, fixtures and public hardware.

The common thread: the more vertical the drive walls, the less the bit wants to climb out under torque. That single idea explains why star and square drives beat Phillips with an impact driver.

The bits to keep on hand

• PH2: several, because Phillips bits wear fastest.
• T25 and T20: for most deck and exterior screws; add T30 and T40 for structural screws.
• SQ2: for construction and cabinet screws; SQ1 for smaller trim screws.
• PZ2: if you assemble European furniture or hardware.

Use impact-rated bits for all of them; the reasons are in impact-rated vs regular bits. Holders, power bits and starter kits are covered in the main impact driver bits guide.

Impact Torx bits on Amazon Square power bits

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