KF centering ring
A CNC machined SS304 centering ring for KF (NW) quick-flange vacuum joints. It sits between two KF flanges, carries the seal in its groove and keeps the two bores aligned. Made in NW16, NW25, NW40 and NW50.
What the ring actually does
A KF joint is held together by a single clamp, but nothing inside it locates the sealing element — that is what the centering ring is for. It drops into the flange bore, carries the seal in its outer groove so the seal cannot shift while the clamp is tightened, and its inner shoulder holds both flange bores concentric.
We machine ours from SS304 bar stock on our own lathes. The seal groove and the locating shoulder are cut in the same setup, so the two stay concentric and the seal seats evenly the whole way round. Sizes are NW16, NW25, NW40 and NW50 — the four that carry most small-bore vacuum plumbing.
- Model
- KF-CR
- Body
- SS304 stainless steel
- Made to order
- 316 on request
- Size range
- NW16 · NW25 · NW40 · NW50
- Connection
- KF / NW (ISO-KF)
Where it gets used
Every valve leak tested.
Each unit is checked for leakage before shipment.
What does a KF centering ring do?
It does two jobs at once. The outer groove carries the sealing element so it cannot shift while you tighten the clamp, and the inner shoulder centres the two flange bores against each other. Without it there is nothing inside the joint locating the seal.
Are KF and NW the same thing?
Yes. KF comes from the German Kleinflansch (small flange) and NW from Nennweite (nominal width). Both refer to the same ISO-KF quick-flange standard, so an NW25 ring fits a KF25 flange.
Which sizes do you make?
NW16, NW25, NW40 and NW50. If you need a size outside that range, send us the flange dimension and we will quote it.
What is the ring made of?
SS304 stainless steel, machined from bar stock. 316 is available on request. Material certificates can be issued on request.
How do I pick the right size?
Match the ring to the flange, not to the tube. An NW25 flange takes an NW25 ring. If your drawing only gives the tube outside diameter, send it over and we will confirm the size for you.