Overview
EN 22857:1989 (Ground thread taps for ISO metric threads - manufacturing tolerances on the threaded portion) specifies manufacturing tolerances for the threaded portion of ground thread taps used to produce ISO metric internal threads. It covers taps for tolerance classes 4H to 8H and 4G to 6G, for both coarse and fine pitches. The standard is based on ISO 2857:1973 with subsequent amendments and applies to the short taps referenced in ISO 529 as well as other ground taps with the same diameters and pitches. Internal threads produced using these taps are conventionally designated as a “nut” in line with ISO 965 terminology.
Key Topics
- Scope and applicability: Tolerances relate specifically to ground thread taps for ISO metric threads (coarse and fine pitches) and apply to short taps per ISO 529 and equivalent ground taps.
- Manufacturing tolerances: Defines how the threaded portion of ground taps must be manufactured to guarantee the intended fit and interchangeability of the internal threads produced.
- Thread tolerance classes: Focuses on taps that produce internal threads in tolerance fields 4H–8H and 4G–6G.
- Terminology alignment: Uses conventional designations such as “nut” for internal threads consistent with ISO 965.
- Conformance: Helps ensure taps manufactured to EN 22857 produce internal threads that meet metric screw thread standards for fit and fit-class expectations.
Applications
EN 22857 is practical for organizations and professionals involved in:
- Tap manufacturers and toolmakers ensuring their ground thread taps meet repeatable manufacturing tolerances.
- Quality assurance and metrology labs verifying tap geometry and compliance before release.
- OEMs and component manufacturers specifying taps that must produce conforming metric internal threads.
- Procurement and standards compliance teams including standards-based requirements in purchase specifications.
- Design and mechanical engineering when selecting tolerances and fit classes for assemblies relying on tapped holes.
Using this standard helps achieve consistent threaded fits, improves interchangeability of components, and reduces assembly problems caused by nonconforming taps.
Related Standards
- ISO 2857:1973 (+A1:1984, +A2:1986) - underlying ISO document on which EN 22857 is based.
- ISO 529 - defines short taps referenced by the scope.
- ISO 965 - general designation and tolerancing of internal threads (use of “nut” terminology).
- National adoption example: SIST EN 22857:2002 (Slovenia).
Keywords: EN 22857:1989, ground thread taps, ISO metric threads, manufacturing tolerances, tap manufacturers, metric screw threads, thread tolerance classes.