TL;DR
- A DK-LOK part number reads: fitting-type code, tube size, thread code, then material suffix.
- Type codes include D (DK-LOK), U (union), L (elbow), T (tee), X (cross), MC (male connector).
- Material suffixes: -S is 316/316L stainless, -B is brass, -C is carbon steel, -SD is super duplex.
- -N designates an NPT pipe thread; the numbers give tube OD and thread size.
A DK-LOK part number tells you everything about the fitting if you know how to read it. This DK-LOK part number decoder walks you through the twin-ferrule code structure block by block: the body prefix, the fitting-type code, the tube and thread sizes, the thread standard, and the material suffix. Learn the pattern once and you order the exact part without digging through a catalog every time. When a code looks ambiguous, verify by the full part number or call us with your service.
How Is a DK-LOK Part Number Built?
Read a DK-LOK number left to right in blocks. The "D" prefix marks the DK-LOK family. Next comes the fitting-type code that tells you the shape and the ends. Then come the size numbers, usually in sixteenths of an inch for fractional tube. A thread code follows on any part with a pipe end. The material suffix closes the number. So a part like DMC8-8N-S reads as: DK-LOK male connector, 1/2 inch tube, 1/2 inch NPT, stainless steel. Break the number into those blocks and it stops looking like alphabet soup.
What Do the Fitting-Type Codes Mean?
The letters after "D" name the fitting shape and its end types. Here are the common body codes you see on twin-ferrule fittings.
| Code | Fitting type | What it connects |
|---|---|---|
| MC | Male connector | Tube to male pipe (NPT/BSPT) thread |
| FC | Female connector | Tube to female pipe thread |
| U | Union | Tube to tube, straight |
| L | Union elbow | Tube to tube, 90 degrees |
| ML | Male elbow | Tube to male pipe thread, 90 degrees |
| T | Union tee | Three tube ends |
| MT / RT | Male run tee / branch tee | Tube ends plus one pipe thread |
| X | Union cross | Four tube ends |
| CAP / P | Cap / plug | Closes a tube end or a fitting port |
| B | Bulkhead variant | Panel or bulkhead mount version |
Codes combine. A male branch tee, a bulkhead union, or a reducing union stacks letters to describe the exact geometry. When two codes could fit what you see stamped, confirm against the full catalog number.
How Do You Read the Size Numbers?
Fractional DK-LOK fittings state tube size in sixteenths of an inch. So "4" means 4/16, which is 1/4 inch. "8" means 8/16, which is 1/2 inch. "12" means 12/16, which is 3/4 inch. On a fitting with a pipe end, the tube size comes first and the thread size second. On a reducer, the larger end usually leads. Metric DK-LOK fittings carry an "M" and state the size in millimeters, so an M12 end takes 12 mm tube. Here is the fractional map.
| Size code | Tube OD |
|---|---|
| 2 | 1/8" |
| 3 | 3/16" |
| 4 | 1/4" |
| 5 | 5/16" |
| 6 | 3/8" |
| 8 | 1/2" |
| 10 | 5/8" |
| 12 | 3/4" |
| 16 | 1" |
What Do the Thread Codes Mean?
Any DK-LOK fitting with a pipe end carries a thread code so you match the mating standard. "N" is the one you see most in the Gulf South.
- N: NPT taper pipe thread, ANSI/ASME B1.20.1. The North American standard.
- R: BSPT (ISO 7-1) taper pipe thread.
- G: BSPP (ISO 228) parallel pipe thread.
- U: SAE straight thread with an O-ring boss on some adapters.
So the "8N" in DMC8-8N-S is a 1/2 inch NPT thread. If your drawing calls a metric or BSP thread and you receive an NPT part, stop and re-check. Thread standards do not cross-thread safely.
What Do the Material Suffixes Mean?
The suffix at the end of the number names the body material. Match it to your media and your corrosion environment.
| Suffix | Material | Typical use |
|---|---|---|
| -S | 316 / 316L stainless steel | Refinery, chemical, general instrumentation |
| -B | Brass | Low-corrosion utility, air, water |
| -C | Carbon steel | Hydraulic and non-corrosive service |
| -SD | Special / higher alloy variant | Duplex or upgraded service. Verify by full part number. |
Most instrumentation you spec in a plant carries the -S stainless suffix. When you see -SD or another extended suffix, confirm the exact alloy before you order, because special variants ship on their own lead time.
How Do You Decode a Full Example Part Number?
Put the blocks together and any number reads clean. Take DMC8-8N-S. The "D" is DK-LOK. "MC" is a male connector, so tube on one end and male pipe thread on the other. The first "8" is the tube size in sixteenths, which is 1/2 inch. "8N" is the thread block, a 1/2 inch NPT taper thread. "-S" is the material, 316/316L stainless steel. Now try a union elbow: DL6-S reads as DK-LOK union elbow, 3/8 inch tube on both ends, stainless. And a union tee DT4-S is a DK-LOK union tee with three 1/4 inch tube ends in stainless. Practice on a handful of numbers and the pattern locks in. When a number stacks extra letters for a reducer or bulkhead version, slow down and confirm each block against the catalog before you order.
For related products, browse our DK-LOK tube fittings or explore more in our resource library.
Frequently Asked Questions
What does the "D" at the front of a DK-LOK part number mean?
The "D" marks the DK-LOK product family. The letters right after it name the fitting type, such as MC for a male connector.
What does -S mean on a DK-LOK fitting?
-S is the material suffix for 316/316L stainless steel, the standard choice for refinery and instrumentation service.
How is tube size shown in a DK-LOK number?
Fractional fittings use sixteenths of an inch, so 4 is 1/4 inch and 8 is 1/2 inch. Metric fittings carry an M and state millimeters.
What thread does "N" mean?
"N" is NPT taper pipe thread to ANSI/ASME B1.20.1. R is BSPT and G is BSPP. Match the code to your mating thread.
What if the part number does not match anything I expect?
Verify by the full catalog number. Stacked codes describe reducers, bulkheads, and special variants. Send us the number and we confirm it.
Order the Exact DK-LOK Part from Collins-Oliver
Collins-Oliver is your authorized DK-LOK distributor in Baton Rouge, stocking twin-ferrule fittings for refineries, petrochemical plants, and instrumentation shops since 1986. Read us the number or describe the fitting, and we pull the right part. Call (225) 922-9324 or (800) 247-5756, or email info@collins-oliver.com for a quote.