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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? · 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

Also called: cf flange dimensions, conflat flange bolt circle, cf 2.75 flange od, dn40cf dimensions, cf 4.5 flange bolt pattern, cf 6 inch flange, conflat flange size chart, cf35 flange, cf63 bolt circle, cf100 flange, cf16 flange 1.33, uhv flange bolt pattern, ISO 3669 cf flange

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. Mating features

length: 203.0 mm
width: 203.0 mm
height: 6.0 mm

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 The standard is ISO 3669 (the 2020 edition is marked withdrawn, revised as ISO 3669:2026; its summary prints a knife edge height 0.65 ± 0.05 mm; no other numbers of it were readable).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.

ConFlat (CF) knife-edge vacuum flanges to ISO 3669: flange OD, bolt… size chart

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	—

Mating features

Drawn at the exact size. Open press, slide, run and socket features by your process's clearance (tolerances by process); leave designed gaps and clamp fits 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-*

Where the files are

Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.

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	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	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	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	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	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	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)	STEP, IGES, PDF	McMaster-Carr site terms: personal design use, no redistribution verify

Xem scan

File coming

No downloadable true-size file yet: the published figures do not fix the whole shape, and Xem never guesses a number. A measured scan is planned; request it and it moves up.

Let your AI pull this. Add https://xemstudio.com/mcp to Claude, ChatGPT, Cursor or any MCP client (free, no account, one minute) and it can look up exact sizes, mating fits and free STEP/STL from every chat.

Set it up →

Plain text: sheet.txt · JSON: /api/geometry?object=conflat-cf-flanges

Schematic, not to scale.