Overview - ISO 16047:2005 (Fasteners - Torque/clamp force testing)
ISO 16047:2005 specifies standardized conditions and procedures for performing torque/clamp force testing on threaded fasteners and related parts. The standard applies principally to bolts, screws, studs and nuts made of carbon or alloy steel (mechanical properties per ISO 898‑1, ISO 898‑2, ISO 898‑6) with ISO metric threads (M3 to M39) and other mating thread combinations with an ISO triangular profile. It defines how to measure and report tightening characteristics such as clamp force, tightening torque, friction coefficients and yield/ultimate values under controlled conditions.
Key topics and technical requirements
- Scope & exclusions
- Applies to metric threaded fasteners (M3–M39) made of carbon/alloy steel as referenced in ISO 898 series.
- Not applicable to set screws, self‑forming threads or fasteners with additional self‑locking features.
- Measured characteristics
- Clamp force (F), yield clamp force (Fy), ultimate clamp force (Fu)
- Tightening torque (T), yield and ultimate tightening torque (Ty, Tu)
- Torque coefficient (K), coefficient of total friction (μtot), thread friction (μth) and bearing friction (μb)
- Rotation angle (Θ) and torque/clamp force ratio (T/F)
- Test methods
- Determination of coefficients of friction, torque coefficient K (K = T / (F·d)) and T/F ratio using steady application of torque.
- Two test goals: standard conditions (specified test washers/plates and test nuts/bolts) and specific (user‑defined) conditions.
- Apparatus & accuracy
- Testing machine to apply torque/rotation and measure clamp force and torques with accuracy ±2%; angle accuracy ±2° or ±2% (greater).
- For referee testing, use a controlled power tool at constant speed and electronic recording.
- Test fixture must resist permanent deformation under combined clamp force and friction torque.
- Environmental conditions
- Standard tests performed at room temperature; standard range 10 °C to 35 °C unless otherwise agreed.
Applications - who uses ISO 16047 and why
- Fastener manufacturers - characterize tightening behaviour, validate coatings and lubrication, set torque ratings.
- Test laboratories & quality control - verify compliance, produce repeatable torque/clamp force data for certificates.
- OEMs and assembly engineers - derive torque specifications, ensure joint integrity and repeatable preload in production.
- R&D and materials engineers - compare surface treatments, thread designs and friction control strategies.
Practical benefits include improved torque-to-preload predictability, safer joint design, and better torque tool calibration and process control.
Related standards
Keywords: ISO 16047:2005, torque/clamp force testing, fasteners, K‑factor, coefficient of friction, clamp force, tightening torque, bolts, nuts, threaded fasteners.
