ISO 17420-3:2012

Overview

ISO 17420-3:2012 specifies the standardized thread connection between filters and respiratory interfaces for unassisted filtering respiratory protective devices. It defines the mechanical geometry, sealing element characteristics, and required tests to ensure safe, interchangeable connections between filters (male thread) and masks or interfaces (female thread). The standard uses a ∅40×1/7 thread profile and provides pass/fail criteria and GO/NO‑GO gauging and test methods for manufacturers, test labs and regulatory bodies.

Key topics and technical requirements

• Thread profile and dimensions: Standard thread profile ∅40×1/7 with detailed major/minor diameters, pitch and thread height.
• Effective thread length: Male effective length ≥ 14.5 mm; female available length (13.0 ± 0.5) mm.
• Sealing element geometry: Annular sealing element with external diameter ≥ 37.5 mm, internal diameter ≤ 30.0 mm, thickness 2.0 +0.5 mm and a flat surface toward the filter.
• Sealing material properties: Hardness 55–70 Shore A and compression set ≤ 25% after 22 h at 68 °C (ISO 7619‑1 and ISO 815‑1 test methods).
• Circularity tolerances: Thread circularity tolerance 0.15 mm (male major radius and female minor radius).
• Mechanical strength: Connectors must withstand an axial pull force of 100 N for 10 s without separation, breakage or permanent deformation.
• Gauging and tests: Use of GO and NO‑GO gauges (including snap and sector NO‑GO gauges), visual inspection, circularity checks and dimensional gauging as described in the standard.
• Absence of geometric interference: Limits on protrusion of filter or connector faces so interfaces remain compatible and unobstructed.

Practical applications and users

• Manufacturers of filters, cartridges and respiratory interfaces who need to design compatible, interchangeable thread connections.
• PPE designers and product engineers specifying connector geometry and sealing details.
• Testing laboratories and conformity assessment bodies performing dimensional, material and mechanical tests per ISO 17420‑3.
• Procurement and safety managers who require assured compatibility between filters and different mask models (interchangeability).
• Regulatory compliance teams ensuring respiratory protective devices meet international mechanical and sealing requirements.

Related standards

• ISO 17420-2 - Respiratory protective devices - Filtering devices (interface requirements).
• ISO 16972 - Respiratory protective devices - Terms, definitions and units.
• ISO 7619-1 - Rubber - Durometer hardness (Shore).
• ISO 815-1 - Rubber - Compression set.

Keywords: ISO 17420-3, respiratory protective devices, thread connection, filter thread standard, ∅40×1/7, GO/NO‑GO gauge, sealing element, Shore A hardness, compression set, PPE compatibility.