Screwdriver bit types and sizes
A stripped screw is almost never the screw's fault. The usual cause is a bit that is the wrong type, the wrong size, or worn out, spinning under load until the recess rounds off. This page covers the drive profiles you will actually meet, with size charts for each, and the format questions that come with using bits in a drill or impact driver: insert bits versus power bits, holders, and extensions. Everything runs on the same 1/4 inch (6.35 mm) hex shank standardized in ISO 1173 and DIN 3126, which is why one bit set serves every tool you own.
Phillips (PH): the everyday cross
The four-armed cross on most wood and general-purpose screws. Its tapered flanks were designed to let the bit cam out, that is, ride up and out of the recess, once torque gets high, which protected early production-line tooling and still limits overdriving. The price is that Phillips is the most strip-prone profile in common use when the operator keeps pushing past the cam-out point. The WhatDrillBit bit chart and Fine Homebuilding's Phillips versus Pozidriv comparison both describe this designed-in cam-out. Phillips sizes run from PH000 (eyeglass and micro-electronics screws) through PH4 (heavy structural fasteners):
| Phillips bit | Also written | Fits screw gauge | Typical use |
|---|---|---|---|
| PH000, PH00 | #000, #00 | Tiny electronics screws | Phones, laptops, glasses |
| PH0 | #0 | #4 and smaller | Small hardware, hinges |
| PH1 | #1 | #5, #6, #7 | Cabinet hardware, switch plates |
| PH2 | #2 | #8, #9, #10 | The everyday size: most wood and construction screws |
| PH3 | #3 | #12, #14 | Lag and heavy framing hardware |
| PH4 | #4 | 5/16 in and up | Heavy structural, uncommon in DIY |
Chart basis: WhatDrillBit screwdriver bit size chart and DIYself's bit sizes guide; the gauge mapping (PH2 for #8 to #10, PH3 for #12 and #14) matches the classic fastener-supplier reference cited there, and the PH000 and PH00 rows for electronics agree with the Leisto precision-bit catalog.
Pozidriv (PZ): the cross with tick marks
Pozidriv looks like Phillips until you look closely: the screw head carries four small tick marks between the cross arms, and the recess has a second set of ribs at 45 degrees with straighter, more parallel flanks. The extra driving surfaces were added specifically to raise the cam-out threshold, letting PZ recesses carry substantially more torque than the same size in Phillips. Fine Homebuilding and Design World's Pozidriv overview agree on the geometry and on the critical practical point: the two systems are not interchangeable. A Phillips bit enters a Pozidriv screw but contacts only part of the recess and cams out early, rounding the head; a Pozidriv bit will not seat in a Phillips screw at all. PZ is common on European hardware and flat-pack furniture, so if a cross-head screw keeps stripping under a PH bit, check for the tick marks. Sizes run PZ0 to PZ4 (Fine Homebuilding notes driver sizes 0 to 5 exist), paralleling the Phillips numbering: PZ1 for #5 to #7 gauge screws, PZ2 for #8 to #10, PZ3 for #12 and up.
Sources: Fine Homebuilding, Phillips vs Pozidriv; Design World, What are Pozidriv screws; size ranges per DIYself.
Torx (T): the six-point star
The hexalobular star recess, standardized under ISO 10664, engages the bit along the lobes rather than on tapered flanks, so it resists cam-out almost entirely and carries far more torque than any cruciform drive. It is now the default on modern deck, structural, and automotive fasteners. Sizes are a T-number (T1 up past T100 for specialized work); the number is a designation, not a millimeter measurement, corresponding to the point-to-point width of the recess. Common sizes with approximate point-to-point dimensions, per the Oushke and Shuntool Torx charts:
| Torx size | Point-to-point | Typical use |
|---|---|---|
| T6 to T8 | 1.75 to 2.31 mm | Electronics, small appliances |
| T10 | 2.74 mm | Laptop and consumer electronics screws |
| T15 | 3.27 mm | Small automotive trim, electronics |
| T20 | 3.86 mm | Automotive, furniture, GRK-type screws |
| T25 | 4.43 mm | The everyday construction size: deck and structural screws |
| T27 to T30 | 4.99 to 5.52 mm | Lag-scale structural and automotive work |
| T40 | 6.65 mm | Heavy automotive: caliper brackets, seat anchors |
A set covering T10 through T40 handles nearly all construction and automotive Torx work; electronics repair needs the T1 to T10 precision range. External Torx, where the fastener head is itself a star and the tool wraps around it, uses E-numbers (E4 to E44) that do not match T-numbers of the same size.
Sources: Oushke Torx size chart; Shuntool Torx size reference (both list T10 at 2.74 mm through T30 at 5.52 mm); common-size and E-number guidance corroborated by Trail Manual's Torx and spline guide.
Hex: the Allen socket
Hexagonal recesses on socket-head cap screws, furniture bolts, and bicycle fasteners. Hex bits are specified directly by the across-flats size, in metric or imperial, and the two families do not meet: a 5 mm hex is not any imperial size. Common sizes per the DIYself and TrueTips hex guides:
| System | Common sizes | Typical use |
|---|---|---|
| Metric | 1.5, 2, 2.5, 3, 4, 5, 6, 8, 10 mm | Furniture, bicycles, M-series socket screws |
| Imperial | 1/16, 5/64, 3/32, 1/8, 5/32, 3/16, 1/4 in | US-market equipment and socket screws |
Substituting a near-match imperial size for a metric recess (or the reverse) is the leading cause of rounded hex sockets; a 5 mm bit in a 3/16 in socket feels fine right up until it strips.
Square (Robertson): the color-coded square
A square recess with tapered walls that wedges the bit, so the screw stays on the driver, an advantage overhead or in tight spots. It is the standard on Canadian construction screws and common in pocket-hole and cabinet work. Sizes R0 to R4, color-coded, with the screw-gauge mapping per the Aspen Fasteners square drive specification and Lee Valley's Robertson bit listing, which agree exactly:
| Square size | Color code | Fits screw gauge |
|---|---|---|
| R0 | Yellow | #3, #4 |
| R1 | Green | #5, #6, #7 |
| R2 | Red | #8, #9, #10 |
| R3 | Black | #12, #14 |
| R4 | Blue | #16 and up |
Sources: Aspen Fasteners square drive specification (ANSI dimensions); Lee Valley Robertson drive bits; TE-Tools lists the same #0 to #4 range on 1/4 in hex shanks.
Slotted, and the security outliers
The flat blade still appears on terminal screws and decorative hardware. It cannot self-center and slips laterally under torque, which is why it has faded from structural use; blade widths run roughly 3 to 12 mm and should match the slot width closely. Beyond the mainstream six profiles sit the security and specialty drives: security Torx with a center pin, spanner, tri-wing, and clutch heads, mostly encountered in equipment where the manufacturer would prefer you not opened it. A generic 30-piece security bit set covers nearly all of them.
Bits for drills and impact drivers: insert, power, extension
Every bit above fits every power tool the same way: a 1/4 inch hex shank per ISO 1173, into a bit holder, a keyless chuck, or an impact driver's quick-connect collet. The formats differ:
- Insert bits are the short ones, 1 inch / 25 mm, meant to live in a separate magnetic bit holder or the tool's collet. Cheapest, quickest to swap, and the standard refill format; Wiha's catalog and the Vessel insert-bit listing both build their lines around 25.4 mm shanks.
- Power bits are one-piece bits 50 mm to 150 mm long (Wiha lists 50, 60, 110, 127, and 150 mm Phillips power bits) with the drive tip and shank integral. Stiffer than a holder-and-insert combo, and the right choice for recessed or deep-pocketed fasteners where a 1 inch bit cannot reach.
- Bit holders and extensions turn insert bits into power bits: a 1/4 in hex shank with a ball-detent or magnetic receiver on the end, commonly 3 inch or 6 inch long, per the Build-Construct insert-versus-power-bit comparison. Wobble versions add angle for fasteners that are not in line with the tool.
- Impact-rated bits are the ones with a torsion zone, a narrowed flexing section that absorbs the hammer blows of an impact driver. AIMS Industrial's guidance is blunt: standard non-impact insert bits in an impact driver can shatter. If you own an impact driver, buy bits marked impact-rated; see our impact driver vs drill comparison for whether you need the tool at all.
Material matters at this tier too: S2 tool steel bits at roughly HRC 58 to 62 hold their tips under repeated torque loads better than softer chrome-vanadium, which deforms and transfers load onto the recess corners. TrueTips and the AliExpress Phillips-bit sizing guide both make S2 the recommendation for power-driver use.
Sources: AIMS Industrial, insert vs power bits; Build-Construct, 1-inch insert bits vs power bits; TrueTips hex bits guide; Vessel insert bits catalog (DIN 3126 / ISO 1173); Wiha Phillips insert and power bit catalog via Digi-Key.
Quick identification, and fitting tips
The two profiles people genuinely confuse are Phillips and Pozidriv: tick marks between the cross arms mean PZ, a plain cross means PH. Torx is unmistakable, hex is a hexagon, square is a square. The fitting rule is the same for every type: the correct bit drops in and seats fully without rocking, and a bit that wobbles when you push down is the wrong size or the wrong profile. Replace any bit with visibly rounded tip corners; a worn bit destroys screw heads faster than any wrong size. When driving with a drill rather than a dedicated driver, the clutch does the protection work; our torque settings chart maps tasks to clutch numbers, and the companion drilling-side reference is the drill speed chart by material.
Related
For drilling rather than driving, see drill bits by material, the drill speed chart, and the countersink size chart for seating flat-head screws flush. For the tools themselves, the comparison table and buying guide cover what to look for in a drill or impact driver.