ISO 4156-2:2021

Overview

ISO 4156-2:2021 - "Straight cylindrical involute splines - Metric module, side fit - Part 2: Dimensions" specifies geometry and inspection dimensions for the design, manufacture and inspection of straight (non‑helical) side‑fitting cylindrical involute splines. The standard defines limiting dimensions, tolerances, common manufacturing errors and their effects on fits between coaxial spline elements. Linear dimensions are in millimetres and angular dimensions in degrees.

Key topics and technical requirements

• Geometry and inspection tables: Detailed geometry and inspection-dimension tables (Tables 1–148) for a wide range of modules and pressure angles.
• Pressure angles and modules: Nominal pressure angles included are 30°, 37.5° and 45°, with module series specified for each angle (e.g., 0.5, 0.75, 1, 1.25 ... up to 10 for 30°/37.5°; 0.25 to 2.5 for 45°).
• Limiting dimensions and tolerances: Specified maximum/minimum diameters, tooth thicknesses, space widths and form diameters; tabulated tolerances and permissible manufacturing deviations.
• Inspection methods and symbols: Definitions for measurement methods such as measurement over balls/pins (M, MRe), span and k‑tooth measurements (W), and related symbols (D, Db, Fi, Ri, S, E). Annex A gives inspection dimensions for span measurement.
• Fundamental deviation "h": The specified external spline diameters and inspection values are valid for fundamental deviation “h”. For other fundamental deviations, diameters/tooth thicknesses are calculated using formulae in ISO 4156‑1 and inspection dimensions per ISO 4156‑3.
• Effects on fit: Tables and notes describe how manufacturing errors and tolerances influence clearance, sliding and interference fits for mating shafts and hubs.

Practical applications and typical users

This part of ISO 4156 is essential for anyone involved in the lifecycle of splined connections:

• Mechanical designers and engineers specifying splined shafts and hubs for power transmission.
• Manufacturers producing straight involute splines - to set tooling, broaching, hobbing and grinding processes.
• Quality and inspection teams using the standard measurement definitions and tables to verify conformance (span measurement, ball/pin checks, tooth thickness).
• Procurement and specification authors ensuring interchangeability and correct side‑fit behavior in assemblies (clearance/sliding/interference).
• Standards bodies and CAD/data libraries who provide standardized geometry for electronic data.

Related standards

• ISO 4156‑1 - Generalities and formulae for spline geometry.
• ISO 4156‑3 - Inspection dimensions (used to compute inspection values for non‑“h” deviations).

Keywords: straight cylindrical involute splines, metric module, side fit, ISO 4156-2:2021, spline dimensions, inspection dimensions, pressure angle, module sizes, spline tolerances.