ISO 6624-3:2017

Overview

ISO 6624-3:2017 - "Internal combustion engines - Piston rings - Part 3: Keystone rings made of steel" specifies the essential dimensional features and designation rules for steel keystone piston rings. The standard covers keystone ring types T, TB, TBA, TM, K, KB, KBA and KM, for nominal diameters from 70 mm up to and including 160 mm, intended for reciprocating internal combustion piston engines. This second edition updates technology coverage (including PVD rings) and complements the general specifications in ISO 6621‑4.

Key topics and technical requirements

• Ring types and geometry: Defines straight-faced, barrel-faced (symmetrical and asymmetrical), and taper-faced keystone ring forms, including 6° (T-series) and 15° (K-series) side angles.
• Dimensional tables and figures: Includes detailed tables and figures (e.g., Tables 1–3, Tables 4–9, Figures 1–15) that specify widths, tapers, edge radii and other essential dimensions.
• Tolerances and manufacturing notes: Specifies side angle tolerances (non-cumulative), machining features (ground, lapped or partly cylindrical surfaces), and special notes for plated or coated rings.
• Materials and surface treatments: Examples and designation formats reference steel subclasses (e.g., martensitic and alloyed steels) and surface treatments such as chromium plating, nitriding, PVD, and spray coatings, with minimum thickness/depth callouts where applicable.
• Force factors and performance data: Tables provide force factors and ring forces (e.g., Tables 11–14) to support sealing and friction calculations.
• Designation system: Standardized ring designation format (type, diameter, width, material subclass and coating codes) for consistent ordering and documentation.

Practical applications and users

ISO 6624-3:2017 is applicable for:

• Engine designers and OEMs selecting keystone ring geometry and surface treatment for combustion sealing, oil control and wear life.
• Piston ring manufacturers for production to standardized dimensions, tolerances and surface specifications.
• Quality and metrology engineers ensuring interchangeability and compliance with dimensional and coating requirements.
• Aftermarket suppliers and repair shops identifying correct ring types by ISO designation.
• Test laboratories using force factors and dimensional data in performance and durability testing.

Using ISO 6624-3 helps improve interchangeability, reduce design ambiguity, and align piston ring manufacturing with industry-accepted standards for internal combustion engines.

Related standards

• ISO 6621‑4 - Internal combustion engines - Piston rings - Part 4: General specifications (normative reference)
• Other parts of the ISO 6624 series and related piston ring standards (ISO 6621, ISO 6622, ISO 6623, ISO 6625–6627)

Keywords: ISO 6624-3:2017, keystone rings, piston rings, internal combustion engines, steel rings, ring dimensions, ring designation, chromium plating, nitrided, PVD.