Complete Guide to Torx Fasteners: Types, Specifications and Applications

Torx (star drive) fasteners, invented by Camcar Textron in 1967, feature a six-lobe star recess designed for high torque transmission, anti-slip performance and tamper resistance. Widely used in electronics, automotive, medical and aerospace industries, they outperform slotted/Phillips screws with larger contact areas and reduced cam-out risk, ideal for automated assembly.

1. Main Types of Torx Fasteners

Standard Torx (Internal): T1–T100, common T5–T50; symmetrical recess, universal tooling.
Torx Plus: Optimized flat contact, ~20% higher torque, better fatigue resistance; for automotive transmissions and robotics.
Security Torx (TR): Central pin prevents tampering; for public facilities, security devices.
External Torx: Protruding star head (like a nut); for racing engines and specialty machinery.
Micro Torx (T1–T8): Tiny sizes for eyewear, watches, precision instruments and mobile devices.

2. Size System: T-Number & Key Parameters

Torx sizes are labeled “T+number” (number = across-flat distance ×100, inch). Common sizes and thread matches:

Torx Size	Across-Flat(mm)	Compatible Thread	Typical Torque(Nm)	Common Applications
T5	1.42	M1.6–M2	0.5–1.2	Mobile phones, precision electronics
T10	2.74	M2–M3	1.5–3.0	Hard drives, laptops, home appliances
T15	3.27	M3–M4	2.5–5.0	Automotive interiors, sheet metal
T20	3.86	M4–M5	4.0–8.0	Chassis, furniture, new energy parts
T25	4.40	M5–M6	6.0–12	Automotive chassis, PV brackets
T30	5.52	M6–M8	10–20	Machinery, rail transit

Standards: ISO 10664, GB/T 2672-2017 (pan head), GB/T 2673 (countersunk).

3. Head & Thread Types

Pan Head: GB/T 2672, round head, large contact area; for enclosures, home appliances.
Countersunk Head: GB/T 2673, flush surface, anti-scratch; for sheet metal, aerospace parts.
Cylinder Head: GB/T 2671.2, low profile, space-saving; for molds, tight spaces.
Self-Tapping: ST thread, no pre-tapping needed; for thin metal, plastic, wood.

4. Materials & Surface Finishes

Stainless Steel 304/316: High corrosion resistance; for medical, food equipment, outdoor PV (316 for better salt spray).
Carbon Steel (Class 8.8/10.9): High strength, cost-effective; for automotive, machinery, steel structures (zinc/Dacromet coated).
Alloy Steel: High temperature and fatigue resistance; for aero-engines, transmissions.

5. Industry Applications

Electronics: T5–T15 micro Torx for phones, laptops, hard drives, tamper-proof and anti-slip.
Automotive: T20–T30, Torx Plus for transmissions, countersunk for body panels.
Medical Devices: 316 stainless steel for surgical instruments, monitors, sterile and corrosion-resistant.
PV/New Energy: T25–T30 stainless/Dacromet bolts, wind-resistant, 25-year outdoor lifespan.
Aerospace: Superalloy fasteners; Boeing 787 uses 50,000+ units for extreme temperature/pressure.

6. Selection & Assembly Guidelines

Exact Size Match: Use T-number matched bits only; mismatching causes slot stripping.
Torque Control: Apply specified torque to avoid breaking or loosening; use torque tools in automation.
Tamper-Proof: Choose security TR Torx for public equipment.
Material Compatibility: 316/Dacromet for outdoors; 316 for medical.
Clean Assembly: Stainless steel for cleanrooms; avoid violent impact on precision parts.

7. Summary

Torx fasteners have become standard in high-end manufacturing due to high torque, anti-slip, tamper resistance and automation compatibility. From microelectronics to aerospace, proper selection of Torx type, size, material and head style significantly improves assembly efficiency and connection reliability.

Complete Guide to Torx Fasteners: Types, Specifications and Applications