Screwdriver Bit

Screwdriver bits fit into a bit holder or tool chuck and are designed to transmit torque to a screw head. Most bits are manufactured from hardened steel and follow standardized shank dimensions to ensure compatibility with a wide range of tools.

Bit sets commonly include multiple tip types (e.g., Phillips, Torx, Slotted) and sizes, making them a compact and versatile alternative to dedicated screwdrivers.

There are many types of screwdriver bits, each corresponding to a different screw drive geometry. Common types include:

• File:Screw Head - Phillips.svg – Phillips (PH) – Cross-shaped tip, designed to cam out under high torque.
• File:Screw Head - Slotted.svg – Slotted (Flathead) – A flat blade; prone to slipping and less common in power tools.
• File:Screw Head - Pozidrive.svg – Pozidriv (PZ) – Similar to Phillips, with 90° contact angles and additional ribs for improved grip.
• File:Screw Head - Torx.svg – Torx (TX) – A six-pointed star shape, designed for high-torque applications.
• File:Screw_Head_-_Hex_Socket.svg – Hex (Allen) – A hexagonal bit, common in machinery and furniture assembly.
• File:Screw_Head_-_Robertson.svg – Robertson (Square) – A square-shaped bit popular in woodworking and Canadian markets.
• File:Screw Head - Torx Tamperproof.svg – Security bits – Variants of the above with tamper-resistant features.

For a more complete list of screw types and matching bits, see List of screw drives.

The vast majority of screwdriver bits use a ¼-inch hex shank (equivalent to 6.3 mm), standardized for compatibility across hand tools, drills, and impact drivers.

There are two primary shank forms:

ISO 1173 and ASME B107.4 define compatible hexagonal shank dimensions for screwdriver bits, including the widely used ¼″ (6.3 mm) interface in form E.

The concept of interchangeable screwdriver bits dates to the late 19th century, with an 1889 U.S. patent for a spiral driver featuring a removable tip. By the early 20th century, bits were already in common use with braces for faster screwdriving. By the late 1920s, companies like Husky Wrench Co. were marketing complete product lines of forged bits and modular handles for heavy-duty applications.

The rise of powered assembly tools in the mid-20th century greatly increased the demand for standardized bit interfaces. Early bit holders were typically proprietary, but manufacturers and industrial users began to push for common specifications. In 1975, the International Organization for Standardization (ISO) published the first edition of ISO 1173, establishing dimensions and drive-end forms for machine-operated screwdriver bits. The following year, the German Institute for Standardization introduced DIN 3126, a closely related national standard that defined hex shank forms such as C and E. DIN 3126 remained widely used until it was officially superseded in 2009 by DIN ISO 1173, harmonizing it with the ISO specification. In the United States, the American Society of Mechanical Engineers published a parallel specification as ASME B107.4, which defines driving and spindle ends for portable powered tools.

Today, the ¼″ hexagonal shank (6.3 mm) defined in both standards has become the universal interface for general-purpose screwdriver bits, supported by a global ecosystem of tools, holders, and accessories.

The widespread use of impact drivers since the late 20th century introduced new performance demands on screwdriver bits. Unlike drills, which apply continuous rotational force, impact drivers deliver intermittent bursts of high torque. This subjects bits—especially at the tip and shank—to repeated shock loading.

In response, manufacturers developed impact-rated bits designed specifically to withstand these stresses. According to Wiha Tools, Bosch, and Milwaukee Tool, common features include:

• Torsion zones that flex to absorb torque spikes.
• Tougher steel alloys, such as S2 tool steel.
• Ductile heat treatment to reduce brittleness.

Standard bits typically share the same ¼″ hex shank (e.g., ISO Form E 6.3) but often fail prematurely in impact drivers. Their harder heat treatment improves wear resistance but makes them more brittle, leading to chipping and fatigue cracks under repeated torque.

According to a 2020 review, standard bits may suffice in low- to moderate-torque tasks, but impact-rated bits offer greater durability when driving large fasteners, working in dense materials, or under sustained commercial use.

Impact-rated bits remain backward-compatible with drills and manual screwdrivers, though their enhanced design provides no significant advantage in those contexts.

ISO 1173:2001 defines the standardized dimensions as follows.

File:Form_C_6.3_dimensions.svg

Diagram: Dimensions for Form C 6.3, 8 and 12.5

File:Form_C_4_dimensions.svg

Diagram: Dimensions for Form C 4

Iso 1173:2001 Form C Dimensions, dimensions in millimeters

File:Form_E_6.3_dimensions.svg

Diagram: Dimensions for Form E

Iso 1173:2001 Form E Dimensions, dimensions in millimeters

Note, ASME B107.4 defines two further sizes that are not covered by ISO1173:2001. These are 15.88 mm (5/8 inch nominal) and 19.05 mm (3/4 inch nominal).

ASME B107.4 additional hex shank sizes, dimensions in millimeters

• List of screw drives

• Screwdriver
• Drill bit
• Impact driver

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|title=Popular Mechanics Encyclopedia of Tools & Techniques

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}}

ISO 1173:2013 – Assembly tools for screws and nuts — Drive ends for hand- and machine-operated screwdriver bits and connecting parts – Dimensions, torque testing.

{{Cite web |title=ASME B107.4-2019 – Driving and Spindle Ends for Portable Hand, Impact, Air, and Electric Tools (Percussion Tools Excluded) |url=https://www.asme.org/codes-standards/find-codes-standards/b107-4-driving-spindle-ends-portable-hand-impact-air-electric-tools/2019/pdf|publisher=ASME|access-date=2025-06-01}}

{{Cite web

|title=ASME B107.600-2016 – Screwdrivers and Screwdriver Bits

|url=https://www.asme.org/codes-standards/find-codes-standards/b107-600-screwdrivers-screwdriver-bits

|publisher=ASME

|access-date=2025-06-01}}

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| country = US

| number = 402538

| title = Tool-driver

| inventor= Christopher H. Olson

| publication-date = 1889-04-30

}}

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|title=Henley's Encyclopaedia of Practical Engineering and Allied Trades

|publisher=The Norman W. Henley Publishing Company

|location=New York

|year=1906

|page=190

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|volume=19

|issue=2

|date=August 1927

|publisher=Edward G. Baltz

|location=Philadelphia, PA

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{{Cite web |title=Impact Rated Bits: Dispelling the Myths |url=https://www.protoolreviews.com/dispelling-impact-rated-bits-myths/ |last=Johnson |first=Kenny |date=2020-07-29 |website=Pro Tool Reviews |access-date=2025-06-01}}

DIN 3126 – Verbindungssechskante für Maschinenschrauber-Werkzeuge – Maße (Drive ends for machine-operated screwdrivers – Dimensions). Berlin: Deutsches Institut für Normung. {{in lang|de}}

{{Cite web

|title=Bosch Upgrades its Impact Tough™ Impact Driver Bits for Higher Torque Tools, Delivering 10X More Life Over Standard Bits

|url=https://pressroom.boschtools.com/Impact-Tough-Impact-Driver-Bits

|publisher=Bosch Tools Pressroom

|date=2017-03-14

|access-date=2025-06-01

}}

{{Cite web |title=Wiha Terminator Bit Sets Press Release |url=https://cdn.wihatoolsus.com/pdfs/wiha-tools-press-release-terminator-bit-sets.pdf |publisher=Wiha Tools USA |access-date=2025-06-01}}

{{Cite web

|title=Milwaukee Tool Delivers the Ultimate Fit with New SHOCKWAVE Impact Duty Driver Bits

|url=https://www.milwaukeetool.com/news/press-releases/milwaukee-tool-delivers-the-ultimate-fit-with-new-shockwave-impact-duty-driver-bits

|publisher=Milwaukee Tool

|date=2025-03-17

|access-date=2025-06-01

}}

Category:Woodworking hand tools

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