ISO 6157-1:1988

Overview

ISO 6157-1:1988 - "Fasteners - Surface discontinuities - Part 1: Bolts, screws and studs for general requirements" defines permissible surface discontinuities and inspection principles for bolts, screws and studs used in general applications. It applies to fasteners with nominal thread diameters of 5 mm and larger, product grades A and B, and property classes up to and including 10.9. The standard establishes limits for defects (cracks, bursts, seams, voids, folds, tool marks, damages) and includes an annex sampling plan for acceptance inspection.

Key topics and technical requirements

• Scope and applicability: Covers bolts, screws and studs for general requirements; special or tighter limits (e.g., for automatic assembly) are covered in ISO 6157-3 or must be specified by purchaser/product standard.
• Types of surface discontinuities: Descriptions and causes of
  • Cracks (including quench cracks - expressly not permitted in any location)
  • Forging cracks and bursts and shear bursts
  • Seams and laps (raw material defects)
  • Voids (non-filled pockets from forging/upsetting)
  • Folds
  • Tool marks
  • Damages (dents, nicks, scrapes)
• Quantitative limits (examples given in the standard):
  • Voids: depth h < 0.02·d (max 0.25 mm); combined void area on a bearing face limited to a fraction of total area.
  • Seams/laps: permissible depth up to 0.03·d.
  • Tool marks: surface roughness not to exceed Ra = 3.2 μm (per ISO 468).
  • Forging/shear bursts: width limits specified relative to nominal or head diameter (e.g., 0.06·d on some hex heads, 0.08·d or 0.04·d for circular heads depending on count).
  • Quench cracks: prohibited at any depth, length or location.
  • For some defect types the standard provides formulae tied to the nominal thread diameter - see ISO 6157-1 for exact expressions.
• Inspection and evaluation:
  • Non‑destructive visual/ND testing per sampling plan (annex table for sample sizes).
  • Destructive testing (sectioning at 90° through worst defects) if non‑destructive inspection finds suspect parts.
  • Acceptance criteria: lots are rejected if certain defects exceed allowed limits (e.g., quench cracks, folds at interior corners).

Applications and users

ISO 6157-1 is used by:

• Fastener manufacturers and heat‑treatment shops (quality control and process validation)
• Purchasing and procurement teams specifying acceptance criteria
• Inspection laboratories and QA/quality engineers in automotive, aerospace, heavy machinery, construction and general manufacturing
• OEMs and assemblers concerned about functional integrity and automatic assembly compatibility

Related standards

• ISO 468 - Surface roughness parameters
• ISO 898-1 - Mechanical properties of fasteners
• ISO 2859 - Sampling procedures (inspection levels)
• ISO 3269 - Fastener acceptance inspection
• ISO 6157-3 - Surface discontinuities for special requirements

For exact dimensional ratios, inspection tables and complete acceptance rules consult the full ISO 6157-1:1988 document.