ISO 3408-2:2021

Overview

ISO 3408-2:2021 - Ball screws, Part 2 (Metric series) defines the nominal diameters, nominal leads, nut dimensions and mounting bolts for metric ball screws. This second edition (2021) updates the 1991 edition to reflect current market practice, adds additional dimensions and flange types, and groups ball screws into three standardized series (two internal recirculation series and one external recirculation series). The standard includes tables and figures that specify preferred diameter/lead combinations and detailed mounting dimensions for common nut flange types (B6, B8, B4, A6, C6).

Key topics and requirements

• Nominal diameters and leads: standardized nominal diameters (from small to large, e.g., 4 mm up to 160 mm) and nominal leads (common values up to 50 mm) and the preferred combinations of diameter and lead (Table 1). A general plan is provided for allowable additional combinations when deviations are necessary.
• Mounting dimensions for ball screw nuts: detailed flange geometry, centring and collar options, flat widths, counterbore and thread positions, lubrication port provisions and alternatives (Figures 1–6 and Tables 2–4).
• Nut types and series: three series are defined - Series 1 and 2 (internal recirculation) and Series 3 (external recirculation) - with specific nut flange types (B4, B6, B8, A6, C6) and corresponding dimension tables.
• Mounting bolts and tightening data: mounting bolt pitch circles, recommended bolt diameters and threads, and design data used for bolt tightening and opening-load calculations (tables include bolt sizes and tightening torque references; calculation basis references VDI 2230).
• Terminology and symbols: uses terms from ISO 3408-1 and provides symbol definitions for dimensions (d, P, D, L, etc.).

Practical applications

• Ensures interchangeability of ball screw components across manufacturers by standardizing nominal sizes, leads and nut/flange interfaces.
• Guides machine tool designers, linear motion system engineers and OEMs in specifying correct ball screw geometry and mounting hardware for precision axes, CNC machines, robotics and actuation systems.
• Supports manufacturers and suppliers of ball screws, nuts and mounting hardware in producing compatible, market-conforming products.
• Assists procurement, quality and maintenance teams in verifying compliance and replacing components with compatible parts.

Who should use this standard

• Machine tool designers and mechanical engineers
• Linear motion and motion control system integrators
• Ball screw and bearing manufacturers
• Procurement and maintenance engineers ensuring spares compatibility
• Standards and compliance officers

Related standards

• ISO 3408-1 - Ball screws: Vocabulary and designation (normative reference used for terms and definitions)

Keywords: ISO 3408-2:2021, ball screws, nominal diameters, nominal leads, nut dimensions, mounting bolts, metric series, ball screw mounting, flange types, ball screw standards.