# ConFlat (CF) knife-edge vacuum flanges to ISO 3669: flange OD, bolt circle, hole count and diameter, thickness, tapped thread, 1.33 to 8 in + bolt-pattern templates

> What are the OD, bolt circle and number of bolts of a CF 2.75 in (DN40CF) ConFlat flange?

- Category: Hardware › Vacuum flanges
- Kind: Standard part
- Basis: Neyco's CF flange catalogue table (fixed blank flanges), cross-checked against Kurt J. Lesker's catalogue and two Vacgen listings, read in this session; numbers and bolt-pattern templates only
- Page: https://xemstudio.com/objects/conflat-cf-flanges/ · JSON: https://xemstudio.com/api/geometry?object=conflat-cf-flanges · Plain text: https://xemstudio.com/objects/conflat-cf-flanges/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files CC BY 4.0 or their publisher's license
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

## Overall (mm)

| length | width | height |
|---|---|---|
| 203.0 | 203.0 | 6.0 |

**Exact dimensions.** Every file is drawn at true size with no tolerance added. The holes and pins that meet another part are listed below under Mating features, with the fit each joint needs; open those by your process's clearance before making the part.

## Notes

- A ConFlat (CF) flange is the all-metal UHV flange: a knife edge on each face bites into a copper gasket. North American sizes are named by the flange OD in inches (1.33, 2.75, 4.5, 6, 8 in); European sizes by the nominal tube ID in mm (DN16CF, DN40CF, DN63CF, DN100CF, DN160CF). The standard is ISO 3669 (the 2020 edition is marked withdrawn, revised as ISO 3669:2026; its summary prints a knife edge height 0.65 ± 0.05 mm; no other numbers of it were readable).
- Table: Neyco page F8, 'fixed blank flange' P/N F16, F35, F63, F100, F150; mm. The OD is the column printed D1, the bolt circle PCD, the hole diameter BH and the thickness the column printed A; the extracted text does not define these letters, so they are matched by value to the other sources below. DN as printed by Neyco: 16, 35, 63, 100, 150; 2.75 in is also sold as DN40CF and 8 in as DN160CF.
- Cross-checks: Lesker's catalogue (extracted text, third data column unlabelled) gives 6 holes, hole 0.172 in, tapped 8-32, bolt circle 1.062 in (26.9 mm) for 1-1/3 in; 6, 0.265 in (6.73 mm), 1/4-28, 2.312 in (58.7 mm) for 2-3/4 in; 8, 0.332 in (8.4 mm), 5/16-24, 3.628 in (92.2 mm) for 4-1/2 in; and rows for 2-1/8 in (4 holes, 1.625 in) and 3-3/8 in (8 holes, 2.850 in) that Neyco does not list. Lesker's 6 and 8 in rows were not in the text read. Bolt circles agree within rounding (Neyco 27 / 58 / 92 against Lesker 26.9 / 58.7 / 92.2 mm and Vacgen 27 / 58.7 / 181).
- Disagreements, shown not resolved: hole 6.7 (Neyco), 6.73 (Lesker) and 6.8 (Vacgen 70 mm) on the 2.75 in flange; 8.3 (Neyco) against 8.4 mm (Lesker) on the 4.5 in; thickness 12.7 (Neyco A) against 13 (Vacgen B) on 2.75 in, and 22.3 against 22 on 8 in; Vacgen's 34 mm listing prints the tapped thread as M6, Neyco M4 and Lesker 8-32 (M4). The Vacgen 203 mm listing also prints a Ø8.4 mm hole against Neyco 8.3.
- Vacgen's listings add: 70 mm flange: land thickness 4.8, bolt circle 58.7; 203 mm flange: land thickness 9.5. These are a maker's own dimensions for those parts, not standard values. Knife-edge diameter, groove diameter and gasket sizes were not read from any source and are not given.
- Files: CF bolt-pattern templates, one per size, drawn with Neyco's OD, bolt circle, hole count and hole diameter. 6 mm thickness (the catalogue flange thickness is in the table), the central aperture (half the bolt circle) and the first hole position (on +X) are Xem choices; the knife edge, bore and tube are not modelled. Hole position relative to the axis (straddling or on it) is not given by the sources.
- Small flanges are on iso-kf-flanges-nw10-nw50 and large ISO flanges on iso-k-iso-f-flanges-dn63-dn630. McMaster-Carr's vacuum-fittings category is linked for per-part STEP.

## Mating features (exact size; open press / slide / run / socket by your process clearance, leave designed and clamp as drawn)

| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| CF bolt holes | 1.33 in: 6 × Ø4.3 on Ø27; 2.75 in: 6 × Ø6.7 on Ø58 (Lesker 58.7); 4.5 in: 8 × Ø8.3 on Ø92; 6 in: 16 × Ø8.3 on Ø130; 8 in: 20 × Ø8.3 on Ø181 (Neyco; sources differ by 0.1 mm on some holes) | bolts through the mating CF flange's identical pattern, or its tapped holes M4 / M6 / M8 (Neyco) or 8-32 / 1/4-28 / 5/16-24 (Lesker) | slide | cf-* |

## Sizes

| size (OD) | DN (Neyco) | flange OD (mm) | bolt circle (mm) | holes | hole Ø (mm) | tapped thread | thickness A (mm) |
|---|---|---|---|---|---|---|---|
| CF 1.33 in | 16 | 34 | 27 | 6 | 4.3 | M4 | 7.6 |
| CF 2.75 in | 35 (also DN40) | 70 | 58 | 6 | 6.7 | M6 | 12.7 |
| CF 4.50 in | 63 | 114 | 92 | 8 | 8.3 | M8 | 17.4 |
| CF 6.00 in | 100 | 152 | 130 | 16 | 8.3 | M8 | 19.9 |
| CF 8.00 in | 150 (also DN160) | 203 | 181 | 20 | 8.3 | M8 | 22.3 |
| Lesker 1-1/3 in | — | — | 1.062 in (26.9 mm) | 6 | 0.172 in (4.3 mm) | 8-32 (M4) | — |
| Lesker 2-3/4 in | — | — | 2.312 in (58.7 mm) | 6 | 0.265 in (6.73 mm) | 1/4-28 (M6) | — |
| Lesker 4-1/2 in | — | — | 3.628 in (92.2 mm) | 8 | 0.332 in (8.4 mm) | 5/16-24 (M8) | — |
| Lesker 2-1/8 in (not in the Neyco table) | — | — | 1.625 in | 4 | 0.265 in | 1/4-28 | — |
| Lesker 3-3/8 in (not in the Neyco table) | — | — | 2.850 in | 8 | 0.332 in | 5/16-24 | — |

## Where the files are

- Neyco (CF flange catalogue, page F8): [Fixed blank CF flanges F16 to F272: DN, A, D1, GR, PCD, BH, bolt holes count, tapped thread; letters not defined in the extracted text](https://www.neyco.fr/uploads/media/category/0001/03/Vacuum-F-Brides-CF.pdf) — web — Maker catalogue; numbers only
- Kurt J. Lesker (catalogue, extracted text): [Flanges, fittings and components: CF fixed flange standard dimensions (bolts, hole diameter, tapped thread, bolt circle); size lists for KF 1-4 and ISO 1-5](https://www.acomee.com.mx/catalogos/catalogosk/KURT-J-LESKER FLANGES, FITTINGS AND COMPONENTS.pdf) — web — Maker catalogue copy; numbers only. Column letters were not labelled in the extracted text
- Vacgen (CFR34-6 listing): [304L rotatable bored CF flange 34 mm OD (DN16): flange thickness B 7.6, bolt circle F 27, 6 holes of 4.3 mm, tapped thread printed M6](https://vacgen.com/34mm-od-6mm-id-304l-rotable-bored-cf-flange) — web — Maker listing; numbers only
- Vacgen (CF70-41 listing): [304L fixed bored CF flange 70 mm OD: clear bore A 40, flange thickness B 13, land C 4.8, counter bore D 41.3, bolt circle F 58.7, clear holes 6.8 mm, 6 holes, tapped M6](https://vacgen.com/70mm-od-41mm-id-304l-fixed-bored-cf-flange) — web — Maker listing; numbers only
- Vacgen (CF203 listing): [316LN fixed bored CF flange 203 mm OD: OD 203, flange thickness B 22, land C 9.5, bolt circle F 181, 20 holes of 8.4 mm, tapped M8](https://vacgen.com/203mm-od-153mm-id-316ln-2d-fixed-bored-cf-flange) — web — Maker listing; numbers only
- ISO (iTeh catalogue): [ISO 3669:2020 Vacuum technology - Dimensions of knife-edge flanges (withdrawn, revised as ISO 3669:2026); knife edge height 0.65 ± 0.05 mm](https://standards.iteh.ai/catalog/standards/iso/02727f16-c080-4811-8a11-c40453bd9e38/iso-3669-2020) — web — Publisher's page; dimensions are facts
- McMaster-Carr: [Vacuum fittings (KF / ISO flanges) (free STEP/IGES per part, for your own design use; no redistribution)](https://www.mcmaster.com/products/vacuum-fittings/) — STEP, IGES, PDF — McMaster-Carr site terms: personal design use, no redistribution (verify at link)

## Questions

**What is the bolt circle of a 2.75 in ConFlat flange?**

58.7 mm (2.312 in) in Lesker and Vacgen, 58 mm rounded in Neyco; 6 holes of about 6.7 mm, flange OD 70 mm (DN40CF).

**How many bolts does a CF 6 in flange have?**

16 holes of Ø8.3 on a 130 mm bolt circle (Neyco, flange OD 152 mm).

**How many bolts does a 4.5 in CF flange have?**

8 on a 92 mm (3.628 in) bolt circle; hole 8.3 (Neyco) or 8.4 mm (Lesker).

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