ISO 10666:1999

Overview

ISO 10666:1999 defines the mechanical and functional properties required for heat‑treated drilling screws with a tapping screw thread (per ISO 1478) that incorporate a self‑drilling point. The standard ensures screws can drill their own core hole and form a mating thread without distortion or fracture under correct use. ISO 10666 is aimed at manufacturers, test laboratories, quality engineers and specifiers of self‑drilling fastening systems.

Key topics and requirements

• Material: Case‑hardening steel or heat‑treatable steel is required for drilling screws.
• Surface hardness: Minimum surface hardness after heat treatment is 530 HV 0,3 (Vickers).
• Core hardness and tempering:
  • Core hardness ranges 320 HV to 400 HV (different test loads applied for threads ≤ or > ST 4,2).
  • A recommended minimum tempering temperature of 330 °C is specified; the range 275–315 °C should be avoided to reduce risk of tempered martensite embrittlement.
• Case depth: Specified minimum and maximum case depths by nominal thread size (examples):
  • ST 2,9–ST 3,5: 0.05–0.18 mm
  • ST 4,2–ST 5,5: 0.10–0.23 mm
  • ST 6,3: 0.15–0.28 mm
• Microstructure: No ferrite streaks between case and core after heat treatment.
• Hydrogen embrittlement: Electroplated screws require risk management and testing (refer ISO 15330 and ISO 4042).
• Functional tests:
  • Core drilling and thread forming: Screw point must drill the core hole and form mating thread under prescribed axial loads and speeds.
  • Torsional strength: Minimum torque to failure specified by thread size (e.g., ST 2,9 = 1.5 N·m, ST 6,3 = 16.9 N·m).
• Test methods: Vickers hardness per ISO 6507‑1, metallography for case depth and microstructure, drilling + screwing‑in test using low‑carbon steel plates (≤0.23% C, hardness 110–165 HV30), and torsional testing with ±3% torque accuracy.

Applications and users

• Fastener manufacturers and heat‑treaters - to design, heat‑treat and qualify drilling screws.
• Electroplaters and coating suppliers - to manage hydrogen embrittlement and surface treatments.
• Quality control and test laboratories - to perform Vickers hardness, microstructure and torsion/drilling tests.
• Engineers and specifiers in construction, metal fabrication, HVAC, and appliance manufacturing - to select reliable self‑drilling fasteners and ensure compliance with performance criteria.

Related standards

• ISO 1478 - Tapping screw thread
• ISO 6507‑1 - Vickers hardness test
• ISO 15330 - Hydrogen embrittlement preloading test
• ISO 4042 - Electroplated coatings and embrittlement relief

Keywords: ISO 10666, drilling screws, tapping screw thread, mechanical properties, surface hardness, case depth, torsional strength, hydrogen embrittlement.