Superior Fluid Solutions · Cross-Reference
Cross-Referencing a Tee: Run, Branch and Which End Reduces
A tee only looks like one part. Underneath the ports it is three sizes and three functions, and a cross-reference has to match every one of them.
A tee looks like one part until you have to order a replacement for it, at which point it turns out to be three ports, two of which usually match and one of which often does not, plus a shape decision hiding inside the single word “tee.” According to Swagelok®’s own Gaugeable Tube Fittings and Adapter Fittings catalog (MS-01-140), a manufacturer publication, these fittings are catalogued as separate families rather than one shape with options: union tees, tees with a male branch NPT port listed under headings such as “Male Branch, NPT,” and tees with a male run NPT port listed under “Run, NPT.” Getting the family wrong, or getting the odd-sized port wrong, is the most common way a tee cross-reference goes sideways.
Three families hiding inside one word
Start with the union tee, because everything else is a variation on it. It has three tube fitting ends and nothing else: two in line forming the run, one perpendicular forming the branch. All three take a nut and ferrule set and connect straight to tubing, which is the shape most people picture when someone says “tee,” and the shape Swagelok®’s catalog lists first, under a plain “Union” heading.
The other two families exist because a tee sometimes needs to break out of the tube system rather than keep routing more tubing. A branch tee keeps both run ports as tube fitting ends and replaces the branch port with a threaded connection, listed under “Male Branch, NPT.” A run tee does the opposite: the branch stays a tube fitting end, and one run port is threaded instead, listed under “Run, NPT.” The distinction is not cosmetic. A branch tee taps off a gauge or a transmitter mid-line. A run tee breaks the line itself into a threaded connection, most often a valve or an instrument body, while the branch keeps running as tube. Mixing the two up sends the threads to the wrong port.
The catalog goes further and gives each family its own designation code, TTM against the male branch heading and TMT against the run heading, which is a reminder that the family is a catalogued product decision rather than a shape you can talk your way around. Those codes belong to that catalog and nowhere else. Name the family by what the odd port is doing, not by a code or a digit position you half remember, and the rest of a tee cross-reference has somewhere solid to start from.
Why the size order is the part that goes wrong
A tee with three equal ports has one size to confirm. A reducing tee, where one port carries a different tube outside diameter than the other two, has three. Manufacturers publish reducing tees in dimensional tables, listing a tube OD for each of the three positions side by side, but neither manufacturer catalog we reviewed printed a plain-language sentence explaining which column is a run port and which is the branch across every configuration. The table is the instruction, and the columns are not labeled the same way from one catalog to the next. That gap is real, and it is exactly why a cross-reference has to work from the physical part rather than from a string of numbers copied off an old drawing.
In practice this means naming each port by what it does, not by its position in an old part number. Call out the two run ports separately, in the order the tube actually runs, and call out the branch port on its own line, each with a measured tube outside diameter and a measured wall thickness. A callout that just lists three numbers in a row, with no note on which end is which, is the single most common way a reducing tee order ends up in the wrong configuration.
Three ways a tee cross-reference goes wrong before the part ever arrives.
Guessing the branch
Assuming the last number in an old part number is always the branch port, when some catalogs order the columns differently.
Confusing NPT position
Treating a run tee’s threaded port as a branch takeoff, which puts a valve or instrument on the wrong axis entirely.
One measurement, three ports
Recording a single tube OD for the whole tee when one port is actually a different size than the other two.
| Port | What it connects to | Confirm before ordering |
|---|---|---|
| Run port A | In-line tubing on one side of the branch | Measured tube OD, measured wall thickness, tube fitting or NPT end |
| Run port B | In-line tubing on the other side of the branch | Same measurements, checked independently, never assumed equal to Run port A |
| Branch port | The perpendicular takeoff, or the threaded connection on a run tee | Measured tube OD or NPT size, and whether any thread is male or female |
We did not find a published, brand-independent rule for reading size order off a bare part number, so this table is built around what has to be confirmed at the fitting itself rather than around a decoded number. Superlok® part selection is matched against the ports as measured, with grade and dimensions confirmed per order.
Naming the ports on an existing tee
Work from the installed part. Measure all three ports with a caliper rather than trusting that a reducing tee’s off-size port is the one you remember. Note whether the branch or a run port carries the thread, since that fact alone tells you whether you are looking at a branch tee or a run tee before reading a single digit off a stamped marking. Photograph any legible marking, and record which port sits where on the actual installation, not on a drawing that may have been redlined years ago.
Superlok®’s own machining claim reads: the finest interior surface finish of any tube and pipe fitting on the market, quoted here as Superlok®’s own wording and left at that. Tee configurations are listed in 316 stainless steel, corrosion-resistant enough for sample and gauge takeoffs. Each port’s size, the grade, the working pressure and the paperwork get agreed per order, port by port, with nothing carried over from an old drawing. Start at the tee fittings listing, widen out to the tube fittings catalog, look at crosses if the takeoff turns out to be a four-way, and see the cross-reference overview for how the method carries across shapes. Our certifications page covers documentation and the distributors page covers supply.
Questions about cross-referencing a tee
What is the actual difference between a branch tee and a run tee?
A branch tee keeps both run ports as tube fitting ends and threads the branch port. A run tee keeps the branch as a tube fitting end and threads one of the run ports instead. The threaded port’s location, not its size, is what defines the family.
Can a union tee be used where a branch tee is specified?
No. A union tee has no threaded port at all, so it cannot take the place of a fitting whose design purpose is a threaded connection into a valve, gauge or instrument. The two are different families, not different sizes of the same family.
How do I tell which port is the branch on a tee that is already installed?
Measure it. The branch is the port that departs from the straight line of the run. On a run tee, the threaded port is one of the two in-line ports, not the perpendicular one, which is why measuring the geometry matters more than trusting a stamped number you cannot fully read.
Does a reducing tee always have exactly one different-sized port?
That is the common configuration, but not a universal rule. Some catalogs list tees with two differing port sizes. Confirm against the specific manufacturer’s own dimensional table rather than assuming the common case, and Superlok® availability is confirmed per order.
What should I send you to cross-reference an existing tee?
Measured tube OD and wall thickness for each of the three ports, a note on which port carries any thread and its size, and a photo of the body if a marking is legible. We will work through the cross-reference from there.
Superior Fluid Solutions
Name the ports by their job, never by their position.
Sources
- Swagelok, “Gaugeable Tube Fittings and Adapter Fittings,” MS-01-140 (manufacturer publication), supports the catalogued distinction between union tees and tees listed under “Male Branch, NPT (TTM)” and “Run, NPT (TMT),” the designation codes quoted for each, and that reducing tee ports are published as dimensional tables rather than as a plain-language reading rule. swagelok.com
- Swagelok, “An Installer’s Pocket Guide for Swagelok Tube Fittings,” MS-13-151 (manufacturer publication), supports that pull-up is published as a wrench turn count measured from a marked position for each size, which is the procedure that applies at every one of a tee’s ports individually rather than once per fitting. swagelok.com
Technical note: the sources above establish how one manufacturer catalogues union, branch and run tees, and confirm that reducing tee ports are published as dimensional tables rather than as a single plain-language reading rule. The designation codes quoted belong to that catalog alone and are not a key to any other manufacturer’s numbering. They do not establish that a part from one manufacturer performs the same as a part from another, they do not establish that components may be assembled together across brands, and they do not certify a pressure rating for your service. Superlok® grade, pressure rating and documentation are confirmed per order.
Trademark disclaimer: Swagelok® is a registered trademark of Swagelok Company. Superlok® is a registered trademark of BMT Co., Ltd. Superior Fluid Solutions is not affiliated with, authorized by, endorsed by or sponsored by either company, and the marks are used here only to identify the products they name. Cross-references are made by form, fit, and function only.
