Via Silvio Pellico, 60
Phone:+39 041 462471


Working principle


The S-LOK ferrule fitting of four precision engineered parts designed to provide secure leak-proof joint capable of satisfying high pressure, vacuum and vibration application.

  • The back ferrule provides a strong mechanical and antivibration hold on the tube.
  • Fine pitch, silver plated nut ensure no galling.
  • Pressure seal by front ferrule on tube body.
  • Deep tube abutment and close tolerance of nut and body for accurate tube alignment.

Fittings are supplied complete and ready for use.
The front ferrule swages onto the tubes as it moves down the cone of the body creating a pressure/vacuum-tight seal on both tube and the body by the interface pressure and surface finish of mating components. The back ferrule then deform inwards in the cone of the front ferrule, forming into the tube and creating a strong mechanical hold on the tube.
The internal diameter of body and nut are closely controlled diameters which constrain the tube within close tolerance of its axis ensuring accurate alignment within the assembled fitting.

Quality assurance

Quality assurance procedures conform fully with ISO 9000-1994.

Product Specification

The S-LOK instrumentation fittings are widely used in chemical, petrochemical and other industries. The fittings are conform fully to the specification issued from the greatest industries.


The S-LOK fittings has been specifically designed for use on instrumentation, process and contro1 systems, together with equipment employed in chemical and petrochemical. The S-LOK fittings has also found extensive applications in other fields where e very high quality tube fitting is required.


The S-LOK fittings are available in AISI 316, AISI 316L, Brass, 6M0, Monel, Hastelloy C, Incoloy 825, lnconel 600.
Straight fittings are machined from cold finished bar stock and shaped bodies are machined close grain forging. The raw material used fully conform to the chemical requirements of one or more of the specification listed below.



The S-LOK fittings do not twist the tube during installation.
The fitting design ensures that al1 make and remake loading is transmitted axially to the tube. Fitting make-up is eased due to e silver plating of the tube nut threads, which acts as an effective lubricant and prevents galling

No distortion

In make-up, there is no undue force in an outward direction to distort the fitting body or ferrules to cause interference between the ferrules and the nut.
This assures that the nut will back off for disassembly and permits a greater number of end remakes.


Positive, reliable connections with S-LOK fittings have been qualified with exhaustive tests and many year of experience in the manufacture of quality tube fittings. Specific product features such as burnished cones for superior sealing and exacting manufacturing tolerances for consistent product quality, all contribute to the effective sealing of S-LOK fittings.
In tests after repeated remakes S-LOK fittings effected a Helium seal at over 200 Bar. Vibration and impulse tests in the multimillion cycle range prove outstanding seal capability and fatigue resistance.



Selection of tubing

The S-LOK twin ferrule fitting is precision engineered to exacting standards. Careful selection of high quality tubing together with the appropriate S-LOK fitting will ensure the installation of safe, leak free systems. The following tables are intended as a guide to tube ordering. The tube size listed are regularly tested to bursting pressure in both maximum and minimum wall thickness using correctly assembled S-LOK tube fittings, with no sign of leakage or failure at the connections.
For use with tubes of wall thickness other of those listed, recommendations regarding working pressures for S-LOK fittings can be obtained from our Technical Department.
Tube should be fully annealed high quality stainless steel tube to ASTM A-269 or equivalent.
The preferred hardness is 80 Rb or less. If harder tube is used, 90 Rb is the maximum allowed by ASTM A269.

Recommended maximum working bressure for AISI 316 stainless steel and 6M0 with metric tube.


Recommended maximum working bressure for AISI 316 stainless steel and 6M0 with inch tubing.


Pressure test of above tables based on tube in according ASTM A269 - Temperature 20°C / +100°C - Safety factor 4:l

For workina pressures of Monel tubing. moltiply the abobe ratings by 0,8.

Installation instructions

S-LOK tube fittings are supplied completely assembled.

Normal use

Ensure that the end of the tube is cut square and any burrs removed without causing undue chamfering of the tube end.

  • Insert the tube into a S-LOK fitting ensuring that the tube is firmly butted home into the body of the fitting and the nut is finger tight. (Fig.1)
  • With the body firmly held, mark the nut in the finger tightened position and rotate the nut one and a quarter turns from the marked position. The correctly made connection is then completed. (Fig.2)
  • For size up to 3/16” and 4 mm tube fittings only three quarters of a turn from finger tight is necessary.

High pressure applications, high safety factor systems

To allow for possible tolerance variations in tube diameters when the application demands the maximum pressure sealing capabilities of the fitting. It is recommended that the nut is tightened until the tube cannot be rotated by hand.
From this point the nut should then be tightened one and a quarter turns.

Retightening and disassembly

With S-LOK tube fittings the connection can be disconnected and retightened many times and the same reliable, safe leakproof connection obtained.
Holding the body with a spanner, the nut is tightened to the original position and then given a slight extra effort to retain positive sealing. (Fig. 3)