Overview
ISO 7051:2011 defines the characteristics and designation of cross-recessed raised countersunk (oval) head tapping screws. The standard covers tapping screws with thread sizes ST 2,2 to ST 9,5 inclusive and specifies dimensions, head and recess types, material options, mechanical-property references, finishing/coating requirements and acceptance inspection references. It is the authoritative ISO reference for manufacturers, purchasers and quality engineers specifying these fasteners.
Key topics and requirements
- Scope and thread range: Applicable to tapping screws with thread sizes ST 2,2 → ST 9,5.
- Head and recess types: Defines raised countersunk (oval) head geometry and cross-recess forms (Types H, Z and recess numbers 0–4 shown in the standard). Head types C, F, R are illustrated.
- Dimensions and lengths: Dimension tables and figure references set maximum/minimum head, recess and thread-related dimensions (see Table 1 in the standard).
- Materials and mechanical properties: Steel tapping screws reference ISO 2702; corrosion‑resistant stainless‑steel variants reference ISO 3506‑4 (examples: A2‑20H, A4‑20H, A5‑20H). Product grade and tolerances follow ISO 4759‑1.
- Finish and coatings: Electroplated coatings per ISO 4042; non‑electrolytic zinc‑flake coatings per ISO 10683; passivation of stainless fasteners per ISO 16048.
- Thread and recess standards: Thread form per ISO 1478; cross recess and penetration depth references include ISO 4757 and ISO 7721‑2.
- Acceptance and inspection: Acceptance inspection rules per ISO 3269; general fastener requirements per ISO 8992.
- Designation format: Clear naming convention, e.g.
- Tapping screw ISO 7051 - ST 3,5 × 16 - St - R - Z
- Tapping screw ISO 7051 - ST 3,5 × 16 - A4-20H - R - H
Applications and users
- Who uses ISO 7051: Fastener manufacturers, procurement/specification engineers, design engineers, quality/inspection teams and suppliers of assemblies that use tapping screws.
- Typical uses: Fastening in sheet‑metal assemblies, appliance and electronics enclosures, light machinery, and other applications requiring a raised countersunk (oval) head and cross‑recess drive where controlled head geometry and mechanical properties are critical.
- Why use it: Ensures interchangeability, consistent mechanical performance, correct head/recess fit for drivers, and compliance with accepted coatings and inspection regimes - reducing assembly issues and supplier disputes.
Related standards (normative references)
Key referenced ISO documents include: ISO 1478, ISO 2702, ISO 3506‑4, ISO 3269, ISO 4042, ISO 4757, ISO 4759‑1, ISO 7721 / 7721‑2, ISO 8992, ISO 10683, ISO 16048, and ISO 225.
Keywords: ISO 7051:2011, cross‑recessed raised countersunk (oval) head tapping screws, tapping screws ST 2.2–ST 9.5, fasteners standard, stainless steel tapping screws, coatings, acceptance inspection.
