ISO 6624-2:2016

Overview

ISO 6624-2:2016 - Internal combustion engines - Piston rings - Part 2: Half keystone rings made of cast iron specifies the essential dimensional features and related characteristics for half keystone piston rings (types HK, HKB, HKBA) made of cast iron. The standard covers nominal diameters from 38 mm to 160 mm and defines geometry, measurement methods, force factors and surface treatment options for rings used in reciprocating internal‑combustion piston engines for road vehicles and other applications.

Key topics and technical requirements

• Scope and ring types: Defines straight‑faced (HK), barrel‑faced (HKB) and asymmetrical barrel‑faced (HKBA) half keystone rings, including designation examples (e.g., Piston ring ISO 6624-2 HK - 90 × 1,5 - MC53/CR2).
• Dimensional tables and figures: Essential dimensions, tolerances and schematic figures are provided in Tables 1–4 and Figures 1–9. Measurement width h is calculated per Annex A.
• Forces and corrections: Table 7 gives nominal tangential and diametral forces; correction factors for coatings, chamfers and non‑standard materials are in Tables 5–6. Baseline force data use grey cast iron with modulus of elasticity ≈ 100 GN/m².
• Surface treatments: Chromium plating (codes CRF, CR1–CR4) and spray coatings (codes SC1–SC4) are specified with minimum thicknesses (e.g., CR1 0.05 mm, CR2 0.10 mm; CRF 0.005 mm). Notes address suitability by ring width (e.g., some finishes not recommended for h ≤ 1.5 mm).
• Chamfers and edge details: Outside/inside chamfer sizes (KA, KI) are tabulated for diameter ranges (38–50 mm, 50–125 mm, 125–160 mm).
• Designation and material classes: Standard shows how to designate rings including nominal diameter, ring width, cast iron subclass (e.g., MC12, MC53) and coating code.

Applications and who uses it

ISO 6624-2:2016 is intended for:

• Engine designers specifying piston ring geometry and sealing performance for automotive and small engine applications.
• Piston‑ring manufacturers producing half keystone cast‑iron rings to consistent dimensions and finishes.
• OEMs and suppliers ensuring interchangeability, correct material selection and surface treatment.
• Quality and test labs verifying dimensional conformity, force factors and coating thicknesses.
• Aftermarket and remanufacturing operations needing standardised replacement ring data.

Using ISO 6624-2 supports reliable sealing performance, predictable elastic forces, and consistent manufacturing tolerances across supply chains.

Related standards

• ISO 6624 (other parts: Part 1, Part 3, Part 4)
• ISO 6621‑4 (referenced general piston ring specifications)

Keywords: ISO 6624-2:2016, piston rings, half keystone rings, cast iron, HK HKB HKBA, piston ring dimensions, chromium plating, force factors, internal combustion engines.