ISO 2320:2015

Overview

ISO 2320:2015 specifies the functional properties and test methods for prevailing torque steel nuts. It defines how to measure prevailing torque and torque/clamp‑force performance for both all‑metal and non‑metallic insert prevailing torque nuts under controlled laboratory conditions (ambient +10 °C to +35 °C). The standard covers metric triangular ISO threads (ISO 68‑1) with common diameter/pitch combinations (ISO 261 / ISO 262), coarse threads M5–M39 and fine threads M8×1–M39×3, and references mechanical and tolerance requirements in ISO 898‑2 and ISO 965‑2.

Key Topics

• Scope and applicability: All‑metal and non‑metallic insert prevailing torque nuts with specified threads and property classes; prevailing torque values are laboratory‑based and actual in‑service torques can vary.
• Definitions: Clear terms such as prevailing torque, prevailing‑on torque, prevailing‑off torque, and seating point are provided to standardize measurement and reporting.
• Combined test method: A single test procedure measures prevailing torque and torque/clamp‑force properties together (see ISO 16047 referenced for torque/clamp force testing).
• Test requirements: Includes proof‑load testing, test clamp‑force levels (typically a percentage of proof load), and installation/removal test protocols (first installation/removal and 5‑removal for type testing or disputes).
• Temperature guidance: Nominal test ambient range is +10 °C to +35 °C; Annex A addresses temperature influence. Service temperature notes: all‑metal nuts may be used −50 °C to +150 °C, non‑metallic insert nuts −50 °C to +120 °C.
• Practical details: Thread gauge and fixture requirements (e.g., thread protrusion through prevailing feature of 3–5 pitches) and allowance for manufacturer lubrication.

Applications

• Used by fastener manufacturers to design and certify prevailing torque nuts against international performance criteria.
• Used by quality and test laboratories to perform standardized prevailing‑torque and torque/clamp‑force testing for acceptance and type approval.
• Used by design, procurement, and reliability engineers in automotive, aerospace, machinery, electronics and other industries where vibration‑resistant or self‑locking nuts are required.
• Helps end users assess reuse implications (prevailing torque decreases with reuse) and select appropriate nut types and property classes for service temperatures and safety margins.

Related Standards

• ISO 16047 - Torque/clamp force testing
• ISO 898‑2 - Mechanical properties of nuts (property classes)
• ISO 965‑2 - Metric thread tolerances (medium quality)
• ISO 68‑1, ISO 261 / ISO 262 - Thread form and pitch tables
• ISO 273 - Clearance holes (relevant for assemblies)

Keywords: ISO 2320:2015, prevailing torque steel nuts, prevailing torque nuts, torque/clamp force testing, ISO 16047, ISO 898-2, prevailing-on torque, prevailing-off torque, test method, fastener standards.