Fluid, piping & valves
Double-ferrule compression fittings
Double-ferrule (twin-ferrule) compression fittings for instrumentation and process tubing, joining tube to tube or tube to pipe thread without welding or flaring, with threaded ends in NPT, BSPT and BSPP.
Overview
A double-ferrule fitting has four parts: the body, a front ferrule, a back ferrule and the nut. When the nut is tightened, the front ferrule is driven into the body and onto the tube to make the seal, while the back ferrule grips the tube and holds it in place. The swaging action accommodates normal variation in tube hardness, wall thickness and dimensional tolerance, and the tube does not rotate during make-up.
The range covers male and female connectors, unions, bulkhead and reducing unions, elbows, tees, crosses, plugs, caps and cylinder adapters. Nut threads are silver-plated to reduce galling, and specials or small batches can be discussed.
Selecting double-ferrule fittings
Match the fitting to the tube first: outside diameter, wall thickness and tube material should be compatible with the ferrule and body material. Then choose the end connection for each port and check that the system pressure and temperature fall within what the tube and fitting combination can handle. For corrosive or offshore service, discuss alloy options before fixing the material.
Range overview
- Types and variants
- Male Connectors
- Female Connectors
- Unions
- Bulkhead Unions
- Bulkhead Reducing Unions
- Elbows
- Tees
- Crosses
- Plugs and Caps
- Male Adapters for Cylinders
- Materials and grades
- SS 304
- SS 316
- Carbon Steel
- Mild Steel
- Brass
- Size range
- Elbow Union: 1/4 in to 2 in
- Bulkhead Union: 1/4 in to 1 in
- Other Sizes to Requirement
- Pressure / temperature
- 1 bar to 600 bar (stainless steel bulkhead union)
- Connections and interfaces
- Double-Ferrule Compression
- NPT
- BSPT
- BSPP
- Other Terminations on Request
- Features
- Four-Part Design: Body, Front Ferrule, Back Ferrule, Nut
- Silver-Plated Nut Threads
- No Tube Rotation During Make-Up
- Suited to Repeated Make and Break
- Specials and Small Batches
Exact specifications depend on the variant, material and size. Confirm ratings and certification against the datasheet or with our engineers before ordering.
Applications
- Instrumentation Tubing
- Process Control Tubing
- Gas Lines
- Hydraulic Lines
- Pneumatic Connections
- Chemical and Fertiliser Lines
Industries
- Oil and gas
- Petrochemical
- Semiconductor
- Power generation
Information that speeds up a quotation
Share what you know. Anything you are unsure of can be marked “not known” — our engineers will help confirm it.
- Tube OD
- Wall thickness
- Connection
- Material
- Pressure
- Temperature
- Media
- Standard
- Test certificate
Need a datasheet?
Add this family to your enquiry list and mention the variant — we will send the relevant technical documents.
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Related solutions and guides
Frequently asked questions
How does a double-ferrule fitting differ from a single-ferrule fitting?
A double-ferrule fitting splits the work between two rings: the front ferrule seals against the body and tube, and the back ferrule grips the tube. A single-ferrule or bite-type fitting uses one ring with cutting edges that bite into the tube. Double-ferrule designs are common on instrumentation tubing; bite-type designs are common on metric hydraulic lines.
What should I send for a quote?
List each fitting by type and quantity, with tube outside diameter and wall thickness, the thread type and size at any threaded end, the material, and the working pressure, temperature and media. If you are replacing existing fittings, a photograph or sample helps confirm the configuration. You can request material test certificates with the order.
Ready to specify double-ferrule compression fittings?
Send the details you have — quantities, sizes, drawings or a part number. Unknowns are fine.