Technical explainer
Instrumentation Fittings: Types and Terminology
Instrumentation fittings create compact, detachable connections around instruments, impulse lines, analyzer systems and control equipment. Correct identification depends on fitting form, tube outside diameter, thread standard, material and service conditions.
By SNG Services · Updated 1 Oct 2026
Common fitting forms
An instrumentation fitting may connect one tube to another, connect a tube to a threaded port, change direction, create a branch, reduce between sizes or close an unused end. Names such as connector, union, elbow, tee, adapter, reducer, cap and bulkhead describe these functions.
- Connectors and adapters for tube-to-thread transitions
- Unions for joining matching or reducing tube sizes
- Elbows and tees for direction changes and branches
- Bulkhead fittings for passing through a panel or enclosure
Tube size and thread are separate details
A fitting can have a tube connection on one end and a pipe thread on the other. Tube outside diameter, tube wall thickness, thread form, nominal thread size and male or female orientation should therefore be recorded separately.
Why visual matching is not enough
Different thread forms and tube dimensions can look similar in a photograph. For a replacement, buyers should confirm markings, dimensions and the existing specification instead of relying only on appearance. Mixing incompatible components can prevent correct assembly.
Service data that completes the requirement
Material, pressure and temperature conditions, fluid compatibility, vibration, installation environment, required fitting form and quantity complete the selection picture. A line-item schedule is the clearest format for a mixed requirement.
Next: prepare the RFQ
How to Select Instrumentation Fittings for an RFQ
Selection guidance for instrumentation fittings, including connectors, elbows, tees, unions, adapters and compression fitting RFQs.
Read the buyer guideFrequently asked questions
What is the difference between a connector and a union?
A connector commonly transitions from a tube end to a threaded connection. A union commonly joins two tube ends. Exact naming can vary, so connection details should accompany the name.
Why is tube outside diameter important?
The fitting must match the actual outside diameter of the tube. Nominal pipe size and tube outside diameter are different measurement systems and should not be substituted.
What should a mixed instrumentation fittings list contain?
For each line item, state fitting type, tube outside diameter, thread form and size, material, pressure and temperature conditions, quantity and any project requirement.