ISO 3669:2026

International
Standard
ISO 3669
Fourth edition
Vacuum technology — Dimensions
2026-06
of knife-edge flanges
Technique du vide — Dimensions des brides à guillotine
Reference number
© ISO 2026
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms. 2
5 Requirements . 2
5.1 Materials .2
5.1.1 Flange .2
5.1.2 Bolt holes .2
5.1.3 Grooves .2
5.1.4 Gasket .2
5.2 Dimensions .2
Bibliography . 7

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
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of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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This document was prepared by Technical Committee ISO/TC 112, Vacuum technology.
This fourth edition cancels and replaces the third edition (ISO 3669:2020), which has been technically
revised.
The main changes are as follows:
— title has been updated;
— Flange type 295CF has been added as it is commonly used for turbo molecular pumps;
— Flange type 350ACF has been added which is compatible with ASTM E2734 flange type 350CF;
— knife edge angle range has been expanded to 0°-40°.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
This edition of ISO 3669 has been revised with the intention of harmonizing its content with ASTM E2734M
in order to ensure compatibility of flanges and gaskets as defined in the two standards. This document is
designed to set the minimum requirements to ensure flange compatibility. Manufacturers’ designs may vary
within the tolerances of this standard to meet specific sealing requirements.
1)
ASTM E2734M was developed from the original ConFlat® flange dimensions and tolerances, as developed
by Varian. The intent of this document is to ensure interchangeability of flanges. It is reasonable to accept
that flanges manufactured to the original Varian specifications are compatible with flanges manufactured
according to this document, even though they might not fall within all tolerances.
1) ConFlat® is the trademark of a product supplied by Varian, Inc. This information is given for the convenience of users
of this document and does not constitute an endorsement by ISO of the product named. Equivalent products may be used
if they can be shown to lead to the same results.

v
International Standard ISO 3669:2026(en)
Vacuum technology — Dimensions of knife-edge flanges
1 Scope
This document specifies the dimensions of fixed or rotatable bolted knife-edge flanges used in vacuum
−11
systems for pressures ranging from atmospheric to as low as 10 Pa.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the
...