ISO 3669-2020 PDF

Full title and description

St ISO 3669-2020 — Vacuum technology — Dimensions of knife-edge flanges. This international standard specifies the dimensional requirements for fixed or rotatable bolted knife-edge flanges used in vacuum systems (from atmospheric pressure down to ultra‑high vacuum levels) to ensure interchangeability and reliable metal-to-metal seals for bakeable and UHV applications.

Abstract

This standard defines the geometry and key dimensions (flange outside diameter, bolt circle, bolt‑hole positions, flange thickness, knife‑edge sealing profile and recommended gasket dimensions) for bolted knife‑edge flanges intended for vacuum service, suitable for pressures ranging from atmospheric down to about 10−11 Pa. The 2020 edition incorporates a corrected figure for the knife‑edge vertical dimension and consolidates a single preferred series of flange dimensions to improve compatibility and interchangeability.

General information

• Status: Published (International Standard; under routine review).
• Publication date: 7 February 2020 (corrected version published May 2020).
• Publisher: International Organization for Standardization (ISO).
• ICS / categories: 23.160 — Vacuum technology.
• Edition / version: 3 (third edition, 2020).
• Number of pages: 7 pages.

Key bibliographic and status details above are those published by ISO and national distributors.

Scope

Specifies the dimensions of fixed or rotatable bolted knife‑edge flanges used in vacuum systems covering pressures from atmospheric down to about 10−11 Pa. The document provides dimensional tables and figures for flange sizes, knife‑edge sealing geometry and recommended gasket dimensions to ensure mechanical interchangeability and effective metal seals for bakeable and UHV joints. It is intended for designers, manufacturers and users of vacuum hardware.

Key topics and requirements

• Dimensional specifications: outside diameters, bolt circle diameters, bolt‑hole positions and flange thickness tolerances.
• Knife‑edge sealing profile: geometry and corrected vertical dimension for reliable metal‑to‑metal seals.
• Gasket recommendations: nominal gasket dimensions and guidance on material selection (metal gaskets such as OFHC copper commonly used).
• Rotatable and fixed bolted flange configurations and permitted bolt‑hole options.
• Compatibility and interchangeability guidance to align with common industrial flange practice (including historical ConFlat® style compatibility notes).
• Notes on material considerations and bakeability for UHV service.

The above topics reflect the standard's clauses, figures and tables that define tolerances and recommended practice for knife‑edge flanges.

Typical use and users

Engineers and designers of vacuum systems, vacuum‑hardware manufacturers and machinists, maintenance and procurement personnel in research laboratories (physics, accelerators, fusion), semiconductor and analytical instrument industries, and any organisation building or maintaining high‑ or ultra‑high‑vacuum systems where reliable, bakeable metal seals and flange interchangeability are required.

Related standards

Documents and standards frequently referenced alongside ISO 3669 include the previous edition ISO 3669:2017 (withdrawn and superseded by the 2020 edition) and other ISO/TC 112 vacuum technology or dimensional standards that address thread tolerances and general flange/tolerance practice. ISO/DIS 3669 is the draft under development intended to replace the 2020 edition. Users should consult related ISO standards on threads and dimensional tolerances when specifying bolt holes and mating hardware.

Keywords

knife‑edge flange, vacuum flange, ConFlat, CF, UHV flange, metal gasket, flange dimensions, bakeable flange, vacuum technology, ISO 3669:2020.

FAQ

Q: What is this standard?

A: ISO 3669:2020 is an International Standard that specifies the dimensions of bolted knife‑edge flanges used in vacuum systems to ensure interchangeability and reliable metal seals for bakeable and ultra‑high‑vacuum applications.

Q: What does it cover?

A: It covers dimensional requirements and sealing geometry for fixed and rotatable knife‑edge flanges (including bolt patterns, flange thicknesses, knife‑edge profile and recommended gasket dimensions) for vacuum service from atmospheric pressure down to about 10−11 Pa.

Q: Who typically uses it?

A: Vacuum system designers, vacuum‑hardware manufacturers and machinists, laboratory staff, semiconductor and instrumentation OEMs, and maintenance/procurement teams responsible for specifying and assembling UHV and high‑vacuum hardware.

Q: Is it current or superseded?

A: As of the publication date 7 February 2020 (corrected May 2020) ISO 3669:2020 is the current published edition; ISO has a DIS (ISO/DIS 3669) under development intended to replace the 2020 edition, so readers should check for a finalized revision if they need the very latest status. (Current date referenced: 1 March 2026 — check ISO or your national standards body for any publication after 2020.)

Q: Is it part of a series?

A: It is part of ISO’s vacuum technology portfolio developed by ISO/TC 112 and relates to other vacuum and dimensional standards; the 2020 edition supersedes ISO 3669:2017. A draft revision (ISO/DIS 3669) has been prepared as a subsequent edition.

Q: What are the key keywords?

A: Knife‑edge flange, vacuum flange, ConFlat, CF, UHV, metal gasket, flange dimensions, bakeable flange, ISO 3669:2020.