# ISO-KF (NW, QF) small flanges to ISO 2861: flange OD, bore, O-ring and centering ring, KF10 to KF50

> What is the outside diameter of a KF10, KF16, KF25, KF40 and KF50 vacuum flange, and what centering ring fits?

- Category: Hardware › Vacuum flanges
- Kind: Standard part
- Basis: ISO 2861:2013 sample pages (d1, d2, d3, O-ring), a reseller table of external and internal diameter, and ANCORP's centering ring table, read in this session; numbers only
- Page: https://xemstudio.com/objects/iso-kf-flanges-nw10-nw50/ · JSON: https://xemstudio.com/api/geometry?object=iso-kf-flanges-nw10-nw50 · Plain text: https://xemstudio.com/objects/iso-kf-flanges-nw10-nw50/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/)

**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

- KF (also NW, QF or the Pneurop quick flange) is the small quick-release vacuum flange: two flanges with a chamfered back are held by a hinged or wing-nut clamp over a centering ring with an O-ring. The standard is ISO 2861; sizes are named by the nominal bore in mm. Values in mm unless stated.
- Standard (ISO 2861 sample pages, nominal bores 10 / 16 / 25 / 40 / 50): d3 (outside diameter of the coupling, flange) is 30, 30, 40, 55, 75; d1 max (outside diameter of the connecting pipe) 14, 20, 28, 44.5, 61; d2 (diameter of the O-ring carrier retainer) 12.2, 17.2, 26.2, 41.2, 52.2; O-ring D 15, 18, 28, 42 (or a 5.33 mm section ring of 40.65 mm for 40) and 55 (or 53.3 mm for 50). The sample's decimals use commas and the tolerance signs were garbled, so tolerances are not given. The sample prints no chamfer angle, rim thickness or tube length, so no flange body is drawn.
- The reseller table prints 'internal diameter' 14, 20, 28, 45, 57 mm (metric) or 12.7, 19.05, 25.4, 38.1, 50.8 mm (imperial tube sizes). These disagree with ISO d1 max for KF40 and KF50 (44.5 / 61), because the sources use different definitions: do not substitute one for the other.
- Centering ring (ANCORP catalogue, inches): dimension A is 0.39, 0.63, 0.98, 1.53, 1.97 in for KF10 to KF50 and B 0.21 in; the catalogue does not define A and B in text, so they are given as printed. Its tubing OD cross-reference is 0.50, 0.75, 1.00, 1.50, 2.00 in (inch tube sizes).
- MKS lists blank KF-10 to KF-50 flanges with a 0.20 in (5 mm) thickness; this is a catalogue thickness for those parts, not a standard value. The flange body is therefore not drawn: the sources read give no rim thickness, chamfer angle or clamp seat.
- McMaster-Carr's vacuum-fittings category is linked for per-part STEP; the flange types are in ISO 2861, available from ISO.

## 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 |
|---|---|---|---|---|
| flange OD | Ø30 (KF10, KF16), Ø40 (KF25), Ø55 (KF40), Ø75 (KF50) (ISO 2861 d3) | hinged or wing-nut KF clamp that grips the flange back | clamp | all |
| centering ring (A) | 0.39, 0.63, 0.98, 1.53, 1.97 in for KF10, 16, 25, 40, 50 (ANCORP, dimension A as printed) | seats between two KF flanges with its O-ring (ISO 2861 O-ring D 15, 18, 28, 42, 55 mm) | slide | all |

## Sizes

| flange | d3 flange OD (mm, ISO 2861) | d1 max (mm, ISO 2861) | d2 (mm, ISO 2861) | O-ring D (mm, ISO 2861) | 'internal diameter' metric / imperial (mm, reseller) | tubing OD (in, ANCORP) | centering ring A × B (in, ANCORP) |
|---|---|---|---|---|---|---|---|
| KF10 (NW10, DN10KF, QF10) | 30 | 14 | 12.2 | 15 | 14 / 12.7 (1/2 in) | 0.50 | 0.39 (A) × 0.21 (B) |
| KF16 (NW16, DN16KF, QF16) | 30 | 20 | 17.2 | 18 | 20 / 19.05 (3/4 in) | 0.75 | 0.63 (A) × 0.21 (B) |
| KF25 (NW25, DN25KF, QF25) | 40 | 28 | 26.2 | 28 | 28 / 25.4 (1 in) | 1.00 | 0.98 (A) × 0.21 (B) |
| KF40 (NW40, DN40KF, QF40) | 55 | 44.5 | 41.2 | 42 (or 40.65 with 5.33 section) | 45 / 38.1 (1-1/2 in) | 1.50 | 1.53 (A) × 0.21 (B) |
| KF50 (NW50, DN50KF, QF50) | 75 | 61 | 52.2 | 55 (or 53.3 with 5.33 section) | 57 / 50.8 (2 in) | 2.00 | 1.97 (A) × 0.21 (B) |

## Where the files are

- ISO (iTeh preview): [ISO 2861:2013 Vacuum technology - Quick-release couplings - Dimensions (sample pages): nominal bores 10, 16, 25, 40, 50; d1 max, d2, d3, O-ring D, O-ring carrier d1, d5, d6](https://cdn.standards.iteh.ai/samples/58069/c1e69744c48b4f1eaed1dbc50f611ae6/ISO-2861-2013.pdf) — web — Standard preview; numbers only
- ProSciTech (support article): [Vacuum flange types and sizes: NW/KF10 to NW/KF50 external diameter and internal diameter (metric and imperial)](https://proscitech.freshdesk.com/support/solutions/articles/44002524967-vac-vacuum-flange-types-and-sizes) — web — Reseller article; numbers only
- ANCORP (catalogue): [ISO quick flange (QF/KF) and large flange (LF) centering rings: ID cross-reference, A and B dimensions in inches (stainless and aluminium centering ring assemblies)](https://future4200.com/uploads/short-url/aRKA89A8sSu693NTJW9PFqCukFa.pdf) — web — Maker catalogue; numbers only
- MKS: [ISO-KF blank flanges with bore: tube OD, bore, thickness 0.20 in (5 mm) for KF-10 to KF-50](https://www.mks.com/f/iso-kf-blank-flanges-with-bore) — web — Maker listing; 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
- 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 outside diameter of a KF25 flange?**

40 mm (ISO 2861 d3). KF10 and KF16 are 30 mm, KF40 is 55 mm and KF50 is 75 mm.

**Is NW the same as KF?**

Yes: NW, KF, QF and DN..KF are all names for the ISO 2861 quick flange, named by nominal bore in mm.

**What O-ring goes in a KF50 centering ring?**

ISO 2861 gives D 55 mm (or a 53.3 mm ring of 5.33 mm section).

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