KF25-Flanged Components and Accessories


  • Quickly Connect to KF25 Vacuum Systems
  • Adapters for Small-Diameter Tubing
  • Straight Pipes and Elbow Joints
  • Wing Nut Clamps and O-Ring Carriers

Application Idea

A KF25C050 Compression Fitting is used to add an empty glass cell to a KF-compatible vacuum system.

KF25WNC

KF25 Wing Nut Clamp

KF25E90

90° Elbow Joint with KF25 Flanges

 

KF25C038

KF25 Flange to Ø0.380"
Compression Fitting Adapter

Related Items


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Features

  • Compatible with ISO 2861 Clamped-Type Quick-Release Couplings
  • Vacuum-Facing Parts Cleaned Ultrasonically
  • All Parts Double-Vacuum Bagged
  • To Request Other KF Flange Nominal Diameters, Please Contact Tech Support

KF flanges are ISO-standardized vacuum fittings that provide a vacuum seal by compressing a rubber O-ring between two mating surfaces. Also referred to as NW, QF, or DN flanges, KF flanges are ideal for quickly assembling vacuum systems thanks to their ease of use, maintenance, and reusability.

We offer KF25 Flange Compression Fitting Adapters to quickly connect glass and metal pipes to KF-compatible vacuum systems. These adapters are constructed from 304 stainless steel for high durability and low outgassing and can connect to pipes with outer diameters of 0.250", 0.375", or 0.500". We also offer KF25-flanged straight pipes and elbow joints for use in assembling vacuum systems. Our straight pipes are available in 50 mm, 100 mm, and 250 mm lengths. Our elbow joints are available with either a 45° or 90° angle.

Our wing nut clamps, O-ring carriers, and blank caps are available in KF16, KF25, and KF40 sizing. Key dimensions of these KF flanges can be found by visiting the KF Flange Sizes tab. Our in-house machine shop allows us to modify or customize components with any standard KF flange. To submit a request, please contact Tech Support.

Video Insight: Working with KF (QR) Vacuum Flange Components
An approach for working with KF flanges is demonstrated, and tips are shared for minimizing leak rates, extending lifetimes, and recognizing when to replace O-rings.

For best performance, a very thin coating of vacuum grease should be applied to any O-ring used in a KF system. This should be done by hand while wearing gloves, leaving just enough grease to cause the O-ring to shine. The O-ring and its mating surfaces should be visually inspected before installation to ensure there is no debris which may prevent proper contact and cause a leak. O-rings should be regularly inspected to spot dry rot, cracking, tearing, or accumulation of debris from normal operation. Replace any O-ring suspected of causing a leak.

KF Flange Sizes

KF flanges are defined by ISO 2861 Clamped-Type Quick-Release Couplings. This specification details the dimensions and tolerances for the five standard KF flange sizes: 10 mm, 16 mm, 25 mm, 40 mm, and 50 mm. These sizes are the nominal bore size of the flanged pipe. The name "KF" derives from the German phrase "Klein Flansche," literally translating to "small flange"; this name was used around the time of the flange's adoption by ISO and DIN, as flanges for pipes larger than 50 mm are more appropriately handled by flanges that deform metal gaskets to create a seal, like CF flanges.

Thorlabs offers from stock 16 mm, 25 mm, and 40 mm KF components and accessories. The dimensions of our flanges are shown in the diagrams below. Our in-house machine shop allows us to modify or customize components with any standard KF flange. To submit a request, please contact Tech Support.

General Diagram of a KF40 Flange
Click to Enlarge

Thorlabs KF40 Flange Measurements
General Diagram of a KF25 Flange
Click to Enlarge

Thorlabs KF25 Flange Measurements
General Diagram of a KF16 Flange
Click to Enlarge

Thorlabs KF16 Flange Measurements
Equivalent Sizes
Absolute Maximum
Inner Diametera
KF Size DN Size NW Size
16 mm KF16 DN16 NW16
25 mm KF25 DN25 NW25
40 mm KF40 DN40 NW40
  • The absolute maximum inner diameter is the inner diameter of the largest pipe that can be welded to the flange. The item's inner diameter is often smaller than the absolute maximum inner diameter.

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KF25 Flange to Compression Fitting Adapters

Item # Compatible Pipe OD Included O-Ring Dimensions
OD ID Thickness Dash #a
KF25C025 0.250" 0.38" 0.24" 0.07" 010
KF25C038 0.375" 0.50" 0.36" 0.07" 012
KF25C050 0.500" 0.63" 0.49" 0.07" 014
  • Society of Automotive Engineers (SAE) Dash Number as Defined in Standard AS568: Aerospace Size Standard for O-rings
  • Quickly Connect Glass and Metal Pipes to KF-Compatible Vacuum Systems
  • Options for Pipe Outer Diameters (OD) of 1/4", 3/8", or 1/2"
  • 304 Stainless Steel Construction for High Durability and Low Outgassing
  • Internal Viton® Fluoroelastomer O-Ring Included

KF25 flanges with compression fittings mount smooth-surfaced pipes to vacuum systems, including metal tubes, such as those used for gas lines, or glass tubes like those found on our empty glass cells or fused silica optical ports. Each fitting contains an internal Viton fluoroelastomer O-ring. When the knurled cap of the fitting is hand tightened, the O-ring compresses and forms a seal around the inserted pipe. For best results, a thin layer of vacuum grease should be applied to the internal O-ring; along with helping to create a vacuum seal, this grease allows an inserted pipe to slide along the O-ring without catching and causing damage. The knurled cap should not be overtightened, as excessive force could cause O-ring buckling, leading to leaks. The sizes of the internal O-rings are given in the table above. Each flange is shipped with a protective plastic cover.

Viton is a registered trademark of The Chemours Company.

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
KF25C025 Support Documentation
KF25C025KF25 Flange to Compression Fitting Adapter for Pipes with OD = 0.250"
$80.92
Today
KF25C038 Support Documentation
KF25C038KF25 Flange to Compression Fitting Adapter for Pipes with OD = 0.375"
$80.92
7-10 Days
KF25C050 Support Documentation
KF25C050KF25 Flange to Compression Fitting Adapter for Pipes with OD = 0.500"
$80.92
Today

KF25 Flange Pipe Fittings

KF25E9045 Diagram
Click for Details

KF25E90 Elbow Pipe Dimensions
KF25E45 Diagram
Click for Details

KF25E45 Elbow Pipe Dimensions
  • Straight Pipes or Elbow Joints for KF25 Vacuum Systems
  • Tube Diameters
    • Straight Pipes: 0.87" (22.1 mm) ID, 0.99" (25.1 mm) OD
    • Elbow Pipes: 0.87" (22.1 mm) ID, 1.00" (25.4 mm) OD
  • 304 Stainless Steel Construction for High Durability and Low Outgassing

We offer straight and angled elbow pipes with KF25 flanges for use when assembling vacuum systems. Details on the angled elbow pipes can be found by clicking on the diagrams to the right. Each flange is protected with a plastic cover during shipping.

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
KF25P05 Support Documentation
KF25P0550 mm Straight Pipe with KF25 Vacuum Flanges
$57.75
Today
KF25P10 Support Documentation
KF25P10100 mm Straight Pipe with KF25 Vacuum Flanges
$60.90
Today
KF25P25 Support Documentation
KF25P25250 mm Straight Pipe with KF25 Vacuum Flanges
$64.05
Today
KF25E45 Support Documentation
KF25E4545° Elbow Pipe with KF25 Vacuum Flanges
$76.65
Today
KF25E90 Support Documentation
KF25E9090° Elbow Pipe with KF25 Vacuum Flanges
$64.05
Today

KF25 Flange-Centering O-Ring Carrier and Wing Nut Clamp

Item # Included O-Ring Dimensions
OD ID Thickness Dash #a
KF25CR-F 1.52" 1.10" 0.21" 320
  • Society of Automotive Engineers (SAE) Dash Number as Defined in Standard AS568: Aerospace Size Standard for O-rings
  • KF25CR-F Centering O-Ring Carrier for KF25 Flanges
    • Holds O-Ring in Place Between KF Flanges
    • Creates Vacuum Seal When Compressed Against KF Mating Surfaces
    • Includes Fluorocarbon O-Ring
  • KF25WNC Wing Nut Clamp for KF25 Flanges
    • Secures Two KF25 Flanges Separated by an O-Ring
    • Fast Hand Tightening; No Tools Required
This animation illustrates a step-by-step procedure for coupling KF flanges.

Thorlabs offers a centering O-ring and a wing nut fastening clamp for mating KF25 flanges to a vacuum system. The angled sides of the wing nut clamp compress the O-ring between the flanges, quickly creating a vacuum seal. The wing nut clamp, which has M5 x 0.8 threads, requires only hand tightening, allowing parts to be quickly swapped in and out of a KF-flanged system.

For best performance, a very thin coating of vacuum grease should be applied to the O-ring before installation. This should be done by hand while wearing gloves, leaving just enough grease to cause the O-ring to shine. The O-ring and its mating surfaces should be visually inspected before installation to ensure there is no debris which may impede proper contact and cause a leak. O-rings should be regularly inspected to spot dry rot, cracking, tearing, or accumulation of debris from normal operation. Replace any O-ring that is suspected of causing a leak. Additionally, be aware that under vacuum pressure, the KF connection may undergo additional compression, causing the wing nut clamp to loosen. Some additional tightening may be performed, but be careful not to overtighten the clamp, as the wing nut may become difficult to remove or jammed when the system returns to atmospheric pressure. Do not remove a wing nut clamp while a system is under vacuum.

We also offer KF16 wing nut clamps and O-rings, as well as KF40 wing nut clamps and O-rings.

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
KF25CR-F Support Documentation
KF25CR-FCentering O-Ring Carrier for KF25 Flanges with Fluorocarbon O-Ring
$9.43
Today
KF25WNC Support Documentation
KF25WNCWing Nut Clamp for KF25 Flanges
$8.59
Today

Blank KF25-Flanged Caps

  • 304 Stainless Steel Construction for High Durability and Low Outgassing
  • Blocks Unused Vacuum Ports

Stainless steel KF flange blank caps can be used to protect a vacuum assembly that is not attached to a vacuum system, to block a port during leak testing, or to cap off a port that is not being used on a vacuum chamber body. Each cap is shipped with a protective plastic cover.

We also offer KF16 blank flange caps and KF40 blank flange caps.

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
KF25CP Support Documentation
KF25CPKF25 Blank Flange Cap
$18.63
Today