Shop Tube & Pipe Instrumentation Fittings
Our Superlok instrumentation tube and pipe fittings, double-ferrule compression tube fittings and NPT pipe fittings, are designed for use in high-pressure and critical fluid systems such as aerospace, defense, chemical processing, and medical equipment. These fittings ensure secure and leak-free connections for process measurement and control systems by utilizing a unique design that uses a nut, body, and ferrule to grip the tubing. The double-ferrule style, featuring an inner and outer ferrule, creates a reliable seal by compressing the tubing into place, preventing leaks even under vibration or pressure. These fittings are widely used for their ease of installation, vibration resistance, and dependability across various industries. The fittings are available in multiple configurations in stainless steel (the pipe fittings are 316 stainless), offering versatility for any application. Proper installation and selection of the right tubing are key for optimal performance.
This section splits instrumentation fittings by end type. Choose tube fittings when at least one end grips tubing with a nut and ferrules, sized by tube outside diameter; choose pipe fittings when the ends are NPT threads, in 316 stainless steel. Each side then narrows by shape. After initial make-up, a gap inspection gauge confirms a tube fitting is tight enough; it is not used on re-tightened fittings. See the Instrumentation Tube Fitting Selection Guide for installation, and the adapter guide to identify NPT threads.
Frequently Asked Questions
What is the difference between instrumentation tube fittings and pipe fittings?
Tube fittings have at least one tube end that grips the outside of the tubing with a nut and ferrules, and they are sized by tube outside diameter. Pipe fittings have NPT ends that seal on the tapered thread, and the pipe fittings here are 316 stainless steel. Tube fittings come in straight, 45°, 90°, tee and cross shapes plus vent protectors, plugs, caps and spare parts; pipe fittings come in straight, 90°, tee, cross, cap and plug shapes.
How does a double-ferrule compression fitting seal?
The fitting has four parts: body, front ferrule, rear ferrule and nut. As the nut is tightened, the two ferrules are driven into the body and compress onto the tubing, sealing and gripping it at the same time. The design is built to stay leak-free under shock, vibration and temperature cycling.
How do I install an instrumentation tube fitting?
Fittings arrive fully assembled; don't take them apart first, as that can introduce contamination. Insert the tube until it bottoms on the shoulder inside the body and finger-tighten the nut. Mark the nut at the 6 o'clock position, hold the body with a wrench and tighten the nut 1-1/4 turns to the 9 o'clock position for 1/4" to 1" sizes, or 3/4 turn to 3 o'clock for 1/16", 1/8" and 3/16". Never assemble or disassemble a fitting while the system is pressurized.
What does a gap inspection gauge do?
It confirms that a tube fitting was tightened enough on initial installation. Hold the gauge next to the gap between the nut and the body: if it won't enter the gap, the fitting is sufficiently tightened; if it does enter, tighten further.
What tubing should I use with instrumentation tube fittings?
Use high-quality, fully annealed stainless steel tubing, seamless or welded per ASTM A269, A213 or equivalent. Hardness must not exceed HRB 90, and HRB 80 or less bends more easily and makes up more easily. The tubing must be softer than the ferrules, free of surface imperfections, cut square and deburred inside and out, with a wall thickness chosen for the pressure rating.
How are instrumentation fittings different from flareless bite-type fittings?
Both seal without flaring the tube. Flareless bite-type fittings use a single ferrule whose cutting edge bites into medium to heavy-wall tubing and suit rugged industrial hydraulic work. Double-ferrule instrumentation fittings are made for precise measurement and control systems that need tighter seals and higher reliability in both low and high pressure service.