A 6-point star bit, also known as a Torx bit or star bit, is a type of screwdriver bit used to fasten or unfasten screw heads with a star-shaped recess. The 6 points on the bit fit into the corresponding 6 points on the screw head, allowing for efficient torque transfer. Star bits are commonly used in automotive, aviation, bicycle, motorcycle, furniture, and computer applications.
Star bits were invented and patented by Camcar Textron in the 1960s as an improvement over slotted and Phillips head screws. The design allows for increased driving torque without damaging the driver or fastener. The star shape is self-centering and resists cam out, stripping, and wear. 6-point star bits are currently standardized as ISO 10664.
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Names and Designations
6-point star bits have several common names and designations:
Torx
Torx is the proprietary brand name used by Camcar Textron and Acument Global Technologies for star bits they manufacture. “Torx” has become a commonly used genericized trademark for cruciform star bits from any brand. The bits are sometimes referred to simply as “Torx drivers.”
Star Bits
Star bits is a generic catch-all term for cruciform screwdriver bits with a star-shaped recess. This encompasses both 6-point and higher point count star bits.
Hexalobular Internal
Hexalobular internal is the technical designation used in standards like ISO 10664 and ASME B18.3. This name refers to the 6 internal lobes on the fastener head that the driver engages.
Hex Socket Screws
Hex socket screws or hex socket drive refers to the type of screw heads that accommodate star bits. This reflects the hexagonal external shape of the screw heads.
Common Sizes
6-point star bits are manufactured in a range standard metric and imperial sizes. The most common sizes are:
| ISO Size | Torx T-Size | Inch Size |
|---|---|---|
| T1 | T1 | 0.031 in |
| T2 | T2 | 0.035 in |
| T3 | T3 | 0.039 in |
| T4 | T4 | 0.046 in |
| T5 | T5 | 0.05 in |
| T6 | T6 | 0.056 in |
| T7 | T7 | 0.062 in |
| T8 | T8 | 0.07 in |
| T9 | T9 | 0.079 in |
| T10 | T10 | 0.086 in |
| T15 | T15 | 0.121 in |
| T20 | T20 | 0.14 in |
| T25 | T25 | 0.168 in |
| T27 | T27 | 0.182 in |
| T30 | T30 | 0.206 in |
| T40 | T40 | 0.265 in |
| T45 | T45 | 0.295 in |
| T47 | T47 | 0.315 in |
| T50 | T50 | 0.339 in |
| T55 | T55 | 0.374 in |
| T60 | T60 | 0.406 in |
| T70 | T70 | 0.472 in |
| T80 | T80 | 0.551 in |
The T1 through T100 Torx sizes correspond to the ISO sizes. The imperial inch sizes are approximations of the ISO dimensions. The most commonly used sizes in general applications are T20, T25, and T30.
Drive Types
6-point star bits are made to fit a variety of manual and powered screwdriver handles with different drive types:
1/4-Inch Hex Drive
1/4-inch hex shafts are the most common drive for star bits. This allows use with standard 1/4-inch hex drive manual handles and power drills.
3/8-Inch Square Drive
Larger star bits intended for high torque applications are made to fit 3/8-inch square drive sockets. This enables use with ratchets, torque wrenches, and impact drivers.
1/4-Inch Square Drive
Some star bits are designed with a 1/4-inch square drive end. This provides a compact drive option for small star bits.
Specialty Handles
Some star bit drivers feature unique drives to retain the bit, such as Torx brand handles using a spring-loaded chuck. This helps prevent bit loss in confined spaces.
Common Uses
Some of the most common applications for 6-point star drive fasteners and matching bits include:
Automotive
Cars, trucks, and motorcycles use star fasteners for assembling mechanical components and body panels. Grade 8 and 10.9 star bolts are typically specified for critical structural joints.
Aviation and Aerospace
Aircraft, satellites, and spacecraft employ star fasteners in aluminium and composite structures for their vibration resistance. The self-centering design eliminates side loads.
Bicycles and Motorcycles
Modern mountain bikes, road bikes, and motorcycles often use lightweight star bolts and screws on the frame, components, and accessories.
Furniture and Cabinetry
Star drive screws are common for assembling furniture, cabinets, and other woodworking. The recess allows flush driving without damaging surfaces.
Appliances and Electronics
Many home appliances, consumer electronics, and office equipment utilize star screws for product assembly and access to internal components.
Medical Devices
Medical equipment like surgical power tools may incorporate star drive connections due to their reliable performance in terms of torque, strips resistance, and sterilization compatibility.
Advantages Over Other Drives
6-point star bits and fasteners offer several advantages over slotted, Phillips, and other common drives:
Higher Torque Capacity
The star shape provides up to 40% increased torque capacity before cam out compared to Phillips heads. The 6 points firmly engage with the driver.
Reduced Wear and Stripping
The thick star points are more resistant to rounding off and stripping than Phillips and slotted drives. This allows longer life and more re-uses.
Improved Centering
The symmetrical star shape automatically centers on the screw axis for easier starting and driving without side slippage.
Superior Holding Power
The greater surface contact between driver and fastener enables excellent gripping power for high tightening and removal torque.
One Size Fits Many
Individual Torx sizes like T25 fit a range of metric and imperial screw sizes, reducing the number of bits required.
Identification and Traceability
The unique star shape allows for clear visual identification and verification of the drive system for quality control purposes.
Licensing and Availability
Torx is licensed to most major fastener companies, ensuring availability of star bits and screws from many brands.
Disadvantages
The main drawbacks associated with 6-point star fasteners include:
Specialized Drivers Needed
Star bits are less common than Phillips and slotted. Not everyone will have a set on hand or know they need star drivers.
Bit Wear and Damage
The thin lobes of star bits are vulnerable to bending or breaking if improperly used at an angle or overloaded.
Bit Loss
The high precision recess can allow star bits to drop out of a driver if not retained with a magnet or chuck.
Limited Sizes Available
Star drive screws are produced in fewer sizes than Phillips or slotted screws. Component design may be limited.
More Expensive Manufacturing
The complex star shaping required for both driver bits and fastener heads increases manufacturing costs compared to simpler options.
Female Socket Limitations
Star shaped socket recesses for bolts or studs are only practical for light duty applications due to the thin walls being prone to distortion.
Conclusion
In summary, the 6-point star bit, commonly known by the Torx brand name, provides distinct advantages in terms of torque transfer, longevity, and performance. This had led to widespread adoption in fields where reliability under high loads is critical like aviation, medical equipment, and automotive manufacturing. The star shape offers clear identification and quality control advantages over traditional drives as well. While requiring some specialized tools, the benefits often outweigh the small additional cost and planning required when specifying star fasteners in a design. With the technology now readily available from industrial fastener suppliers, the unique star drive system will continue growing as an essential fastening solution.