Overview
EN ISO 888:2018 (ISO 888:2012) - Fasteners: bolts, screws and studs - nominal lengths and thread lengths.
This CEN-adopted standard specifies how to define and dimension nominal lengths and thread lengths for bolts, screws and studs with ISO metric screw thread (per ISO 68-1). It is intended for use in product standards, technical drawings and other documents that specify fastener geometry.
Key topics and technical requirements
- Scope: Applies to ISO metric threaded bolts, screws and studs; defines measurement positions and dimensioning rules for lengths and thread lengths.
- Normative references: ISO 68-1 (metric thread profile), ISO 225 (symbols and descriptions), ISO 4753 (thread ends), ISO 4759-1 (tolerances for fasteners).
- Symbols & definitions: Nominal length (l), thread length (b), basic major diameter (d), thread pitch (P) and related terms used consistently for dimensioning.
- Position of lengths: Clear measurement rules for different head and end types:
- Bolts/screws with bearing face - length from bearing face to end.
- Flat countersunk and raised countersunk heads - length from head reference surface to end.
- Concave/serrated bearing surfaces - from effective bearing plane.
- Headless/set screws and fully threaded studs - length from end to end.
- Partially threaded studs/double-end studs - length from thread run-out to nut end, etc.
- Thread length calculation: Default thread length b is calculated unless a product standard specifies otherwise:
- For l ≤ 125 mm: b = 2d + 6 mm
- For 125 mm < l ≤ 200 mm: b = 2d + 12 mm
- For l > 200 mm: b = 2d + 25 mm
- If the unthreaded shank would be ≤ 0.5d, the fastener should be fully threaded.
- Tolerances: Tolerances for lengths and thread lengths are handled according to ISO 4759-1 and also referenced in ISO 225 for particular head/drive types.
Applications
- Standardizes how fastener dimensions are specified on drawings and in product standards, ensuring interchangeability and correct fit.
- Useful when specifying bolted joints, assemblies, fastener procurement, and quality inspection criteria.
- Helps determine when a bolt should be fully threaded versus partially threaded based on length-to-diameter relationships.
Who uses this standard
- Fastener manufacturers and suppliers
- Mechanical designers and OEMs specifying hardware on drawings
- Standards committees and technical authors writing product standards
- Quality engineers and inspectors verifying fastener dimensions
- Purchasing and procurement teams ensuring correct part specifications
Related standards
- ISO 68-1 (Metric screw threads - basic profile)
- ISO 225 (Fasteners - symbols and descriptions)
- ISO 4753 (Ends of threaded parts)
- ISO 4759-1 (Tolerances for fasteners - product grades)
Keywords: EN ISO 888:2018, ISO 888:2012, fasteners, bolts, screws, studs, nominal lengths, thread lengths, ISO metric screw thread, thread length calculation.
