What Is a Flangeless Ferrule Fitting? Design, Sizes and Selection

01What is a flangeless ferrule fitting?

This article covers threaded microfluidic fittings with a separate ferrule. Tubing passes through the nut and ferrule into the instrument port; tightening the nut applies axial compression. The ferrule is the sealing and gripping part around the tubing, not a hose clamp or a sanitary clamp connection.

The HN, HN6, HNF and HNF6 configurations discussed here use M6×1 or 1/4-28 UNF flat-bottom ports. Other geometries, threads and dedicated high-pressure fittings require their own drawings and assembly instructions.

02How does the connection seal?

Slide the correct nut and ferrule onto square-cut tubing in the specified orientation. Insert the assembly into the matching port while keeping the tube end in its required position. As the nut advances, it applies axial force to the ferrule, which grips the tubing and seals against the port. Sealing depends on the components seating correctly, not on thread friction alone.

If the tube end moves, the ferrule is reversed or the tubing OD is wrong, tightening resistance may increase before the sealing surfaces are seated. Additional force does not correct this mismatch and may deform the ferrule or tubing.

Check thread engagement separately from correct seating of the ferrule, tube and port. M6×1 and 1/4-28 UNF are different threads; being able to start a few turns does not prove compatibility. Do not use thread tape or sealant to compensate for a mismatched sealing geometry.

03HN, HN6, HNF and HNF6: thread length and installation space

These FOREACH series differ in head style, material, threaded-section length, overall length and ferrule configuration. Even when thread designation and tubing OD match, compare the dimensions needed for the complete connection.

A 2.4 mm difference in threaded-section length: what must fit?

This difference does not mean that HNF or HNF6 necessarily installs 2.4 mm deeper in the same port. Installed depth also depends on the port and ferrule seating positions. Effective thread engagement is the length over which the internal and external threads actually mate after assembly. Confirm the tube-end position separately.

The nut must compress a correctly seated ferrule while maintaining the thread engagement required by the design. If a shoulder contacts the equipment surface before the ferrule is compressed, the nut may feel fully tight while the joint still leaks. Check the dimensional fit; more torque cannot correct an axial mismatch.

The section and exploded views show the relative positions of the nut, ferrule, tubing and port. They explain the connection layout, not the dimensions or installed depth of every model in the table. Use the corresponding drawing for dimensional checks.

Compare head style and overall length separately

Overall length helps assess axial space, but installed protrusion also depends on insertion depth. HN6 is 15.5 mm long versus 18.1 mm for HN. HNF6 has a compact head yet is 20.0 mm long, compared with 16.5 mm for HNF. For closely spaced ports, compare head diameter; for limited axial clearance, compare overall length, installed protrusion, tightening access and tubing routing.

Then check tubing size groups, materials and ferrules

For example, the HN and HN6 “32” nut size group covers tubing ODs of 2.0, 2.5, 3.0 and 3.2 mm. This does not mean one ferrule fits all four sizes. A 2.5 mm tube still needs a ferrule sized for 2.5 mm OD. HNF and HNF6 use individual tubing-OD configurations rather than the HN grouping rule.

Confirm the complete ferrule part number

HN and HN6 use CL-0X ferrules in OD sizes coded 16, 20, 25, 30 and 32. CL-0 and CL-0X have different geometries; the same “25” size code does not make them interchangeable. For HNF and HNF6, confirm the ferrule against the complete nut part number and approved component list before ordering or assembly.

Select nut and ferrule materials separately. PP and ETFE ferrule options must be confirmed by complete part number. A PEEK or PVDF nut does not mean all wetted surfaces in the connection have that material, and color is not a substitute for material identification.

04How does a ferrule connection differ from a flanged connection?

A flanged design may suit an established flange-forming process or prefabricated tubing assemblies. A ferrule design may suit workflows that avoid flange forming and allow ferrule replacement during maintenance. Permitted pressure, long-term sealing and reconnection limits must come from the specific assembly specifications and validation.

Further reading: Flanged tubing assemblies: design and selection

Compression-ring connections can also avoid tube-end flanging, but their sleeves, washers and assembly method differ from the ferrule arrangement described here. “Flangeless” does not identify one universal sealing structure. See the rigid-tubing fitting guide for a comparison of the three designs.

Rigid-tubing fittings: flanged, ferrule and compression-ring connections

05How to select a suitable fitting

Start with the port, then select tubing size and components

Obtain the complete port thread specification and section drawing to establish the sealing geometry. Use the actual tubing OD to select the nut and ferrule. Tubing ID and length determine internal volume, flow resistance and flow requirements. The nut through-bore is a tubing clearance dimension, not automatically the fluid-path ID.

For a 2.5 mm OD tube with HN6, select the appropriate nut size group and a CL-0X-25 ferrule, then verify the thread, nut material, ferrule material and tubing tolerances. This identifies a candidate assembly; pressure capability, chemical compatibility and installed sealing still require confirmation.

Match materials to the actual fluid and operating conditions

Specify fluid composition, concentration, operating temperature, exposure time and cleaning procedure. Check tubing, ferrule and all wetted components. Also check whether the tubing wall retains its bore and grip under assembly compression. Chemical resistance alone does not validate every wall thickness, OD tolerance or ferrule combination.

Check installation and maintenance access

06Installation and service considerations

Use a tubing cutter suitable for the material to obtain a square end. Remove debris and check for flattening, scratches or deformation. Confirm ferrule part number, orientation and tube-end position, then keep the assembly seated while tightening as specified. Use the method and torque confirmed for that configuration; there is no universal torque for all plastic fittings.

Identify the cause before changing the assembly

These symptoms guide troubleshooting; they do not prove a cause. For example, reduced flow may come from a different tubing ID, cutting debris or bends rather than the fitting type. Compare under controlled conditions to see whether assembly or size changes solve the problem.

Separate ferrule replacement from nut reuse

The ferrules covered here are specified for a single installation; reinstalling them may cause irreversible deformation. Prepare matching new ferrules for maintenance. Inspect the gripped tube end and rework it if required. Assess nut reuse separately by inspecting its threads and load-bearing surfaces; replacing the sealing component does not automatically mean replacing the whole fitting.

Validate the complete connection in the fluidic system

Check leaks, tube movement and flow under defined fluid, temperature and pressure conditions; check air ingress on suction lines. Then cover actual start/stop cycles, pulsation, temperature changes and motion, recording test duration, cycles and allowable leakage. A static pressure-hold pass applies only to those test conditions, not full instrument operation.

Permitted pressure depends on the complete nut, ferrule, tubing and port combination. Do not transfer a dedicated high-pressure fitting rating to HN, HN6, HNF or HNF6. A stronger nut material alone does not increase the allowable pressure of the entire fluid path.

07Frequently asked questions