Overview
EN 26157-1:1991 - Fasteners - Surface discontinuities - Part 1: Bolts, screws and studs for general requirements (ISO 6157-1:1988) is a CEN standard that establishes limits and acceptance criteria for surface discontinuities on common threaded fasteners. The standard applies to bolts, screws and studs with nominal thread diameters of 5 mm and larger, for product grades A and B, and for property classes up to and including 10.9. An annex provides a sampling plan for inspection.
This standard is identical to ISO 6157-1:1988 and has been adopted in national implementations (for example SIST EN 26157-1).
Key topics and technical requirements
- Scope and applicability: Defines which fasteners are covered (diameter ≥ 5 mm, grades A/B, property classes ≤ 10.9).
- Types of surface discontinuities: Describes categories of surface defects that can affect performance and appearance (e.g., laps, cracks, seams, tears) - the standard sets limits for such discontinuities.
- Acceptance criteria: Establishes limits and criteria for when a fastener is acceptable, conditionally acceptable, or rejected due to surface discontinuities.
- Sampling plan: Annex includes a sampling procedure to determine lot conformity without inspecting every item, enabling statistically based quality control.
- Reference to ISO series: Aligned with ISO 6157-1:1988, enabling harmonized inspection and procurement across international markets.
(Note: EN 26157-1 sets the framework and acceptance limits rather than prescriptive manufacturing steps. For detailed inspection techniques or measurement procedures, refer to complementary documents or inspection standards.)
Applications
- Quality control and acceptance testing in fastener manufacturing lines.
- Incoming inspection criteria for suppliers and procurement teams in automotive, construction, machinery and general engineering.
- Defining contractual acceptance criteria in purchase orders and specifications to ensure consistent product quality.
- Guiding inspection plans for third-party auditors and certification bodies.
- Useful for design engineers and maintenance teams who need assurance that fasteners meet surface integrity requirements to avoid fatigue or corrosion initiation.
Who uses this standard
- Fastener manufacturers and production engineers
- Quality assurance and inspection teams
- Procurement and sourcing professionals
- Mechanical designers and reliability engineers
- Third‑party testing and certification bodies
Related standards
- ISO 6157-1:1988 (identical content)
- Other parts of the ISO 6157 series and national adoptions (for full series context and related defect classification)
Keywords: EN 26157-1:1991, fasteners, surface discontinuities, bolts screws studs, ISO 6157-1, sampling plan, nominal thread diameter 5 mm, product grades A B, property class 10.9, CEN.