Truelok® Tube Fittings are comaptible with double ferrule compression type tube fittings for Instrumentations and Process Control industries. The Fittings are manufactured by using SS316. These fittings must be used in accordance with recommended procedure to assure good quality and reliable connections. These fittings are extensively used in a variety of industrial applications especially in Oil & Gas, Petroleum Refining, Power Generation, Chemical Processing, Semiconductor Manufacturing, Pulp & Paper, Research and Development, Bio Technology, Pharmaceutical, Aerospace and many other industries.
Truelok® Tube Fittings are designed and manufactured under stringent Quality Assurance & Process Control System. These fittings provide cost effective, reliable and leak proof connections in Instrumentation and Process Control Sample Systems.
Truelok® double ferrule tube fittings are interchangeable and intermixable with the similar fittings offered by other manufacturers. The dimensional tolerances and surface finishes of Truelok® fittings have been independently verified by numerous experts and have been found to be compatible with double ferrule tube fittings offered by other leading manufacturers.



Truelok® standard Tube Fittings are manufactured by using SS316 Bar Stock in accordance with ASTM A-479 and SS316 Forging in accordance with ASTM A-182. Fittings in other materials are available at special customer’s request.

Operating Temperature:

Truelok® Fittings provide safe and reliable performance from cryogenic temperature to high temperature up to 380 °C.

Working Pressure:

The maximum working pressure of standard fittings when used in conjunction with annealed SS316 seamless tubing per ASTM A-213 or equivalent is shown below.


Fractional Stainless-Steel Seamless Tubing

Allowable working pressures are calculated from an S value of 20,000 psi for ASTM A269 tubing at -20°F to 100°F (-28°C to 37°C), as listed in ASME B31.3, except as noted.

For Welded Tubing

For welded and drawn tubing, a derating factor must be applied for weld integrity:
  • For double-welded tubing, multiply working pressure by 0.85
  • For single-welded tubing, multiply working pressure by 0.80.
NOTE: For gas service, select a tube wall thickness outside the shaded area.
Tube O.D.
Wall Thickness of Tube (inches)
Working Pressure, psig
1/4400051007500 10200
Note: Stainless Steel Tubing should never exceed a maximum surface hardness of Rockwell B 90.


Truelok® double ferrule compression type tube fittings is a mechanism used to both seal and grip tubing. The four components of such fittings are nut, back ferrule, front ferrule, and the body the tube is secured/sealed. These precision componenents are manufactured to a very stringent dimensional tolerance and surface finish ensuring a torque-free and leak-tight seal in all tube fiiting connections.
Proper installation of compression fittings is essential to ensure safety and productive use of fittings. Follow the instructions below to obtain a leak-free seal around the tubing of sample operating systems.
  • Ensure that the end of the tube is cut square and is free from burrs. If necessary, use a commercially available “squaring tool” to square the tube ends. CAUTION: Do not create a chamfer on the tube end.
  • Loosen the nut of the fitting (Do not remove the nut from the fitting).
  • Insert the squared and burr free end of the tube through the nut into the body of the fitting, resting it firmly against the internal shoulder of the fitting.
  • While pushing the tube into the body, tighten the nut to a finger-tight level.
  • Hold the hex portion of the body with an appropriate wrench and tighten the nut with a second wrench to 1 and a 1/4 turn
Over-tightening the nut may result in squeezed tube under the ferrule thus causing the end of the tube to flare. This may jam the tube end into the body of the fittings and create difficulty in disassembling of the fitting’s assembly in the future. Furthermore, over-tightening may result in a permanent damage to the tube and the fitting.

Disassembly and Reassembly of a Compression Tube Assembly:

Truelok® Tube Fittings once assembled properly may be disassembled and assembled repeatedly. The following instructions should be carried out to reassemble a fitting assembly.
NOTE: The ferrules of a properly assembled fitting will remain firmly secured around the tube after the tube fittings assembly has been disassembled.
  • Insert the tubing into the body of the fitting in such a way that the ferrules on the tube engage the inside wall of the fitting.
  • Tighten the nut to a hand-tight condition.
  • Hold the hex portion of the body with a wrench and tighten the nut with a second wrench to 1 and a 1/4 turn.