ISO 16239:2013

Overview

ISO 16239:2013 - Metric series wires for measuring screw threads specifies requirements for thread measuring wires used to determine and calibrate the pitch diameter of common screw threads. The standard covers material, nominal diameters, diameter tolerances, measurement methods and designation. It applies to ISO metric general-purpose threads (M), Unified threads (UN), Whitworth pipe threads (G, R) and ISO metric trapezoidal threads (Tr) with standard pitches, for threads with a small lead angle (< 5°). Typical use is in the calibration of pitch diameters of thread plug gauges.

Key Topics and Requirements

• Material and finish
  • Wires shall be made from stabilized alloy tool steel, free from cracks and defects.
  • Hardness: 760 ± 50 HV5 over the measuring surface.
  • Surface roughness: ≤ 0.4 μm Rz on the measuring surface.
  • Reference temperature for dimensions: 20 °C (per ISO 1).
• Nominal diameters
  • Metric series of best-size wire diameters are listed for M, UN, G/R and Tr threads (tables specify wire nominal diameters matched to pitch or threads per 25.4 mm).
  • For symmetric threads, a best-size wire diameter equals P/(2 cos α/2) (P = pitch).
• Tolerances and grades
  • Two diameter tolerance grades are standardized; choice depends on required measurement uncertainty.
  • Example limit deviations: ±0.5 μm (tight grade) and ±1 μm (coarser grade); maximum permissible differences between wires and along/around a wire are specified.
• Measurement methods
  • Actual diameters measured in three planes (E1, E2, E3) perpendicular to wire axis; two diameters measured in each plane.
  • Direct or comparison measurement (e.g., gauge blocks) recommended per required uncertainty.
  • Roundness/difference around a wire determined by rotating the wire in a 60° groove and applying the specified calculation (difference divided by 1.5).
• Designation
  • Complete marking format: letter “w”, nominal diameter, tolerance grade, serial number and manufacturer/mark (e.g., w 0,231 - 1 No. Name).

Applications and Who Uses It

• Calibration labs and national metrology institutes for validating thread plug gauges and reference wires.
• Gauge manufacturers producing calibrated wire sets and thread gauges.
• Quality and inspection engineers in aerospace, automotive, oil & gas and precision engineering sectors where accurate pitch diameter measurement is critical.
• Use cases: pitch diameter calibration, traceable wire standards, dimensional control of threaded components, and verification of thread gauges.

Related Standards

• ISO 1 - Standard reference temperature for geometrical product specification and verification
• ISO 5408 - Screw threads - Vocabulary

Keywords: ISO 16239, metric series wires, thread measuring wires, pitch diameter calibration, thread plug gauges, wire tolerances, screw thread measurement.