Custom Fittings Machined to Your Print

Which fittings can be made to print?

Custom fittings are quoted as CNC turned parts, from round or hex bar. Wrench flats or a hex cut into round bar are milled features, quoted from the print. A long, slender body suits Swiss screw machining, where the tool cuts next to the guide bushing that supports the bar, however long the part is (source 7).

Beyond the ends named above come unions, reducers and weld nipples. Then there are the parts with no catalog number: an AN-to-ORB adapter in a length nobody stocks, an NPT-to-metric reducer, a barb with a restrictor orifice drilled through it.

When the port has to be welded into a tank or tube rather than threaded into one, that part is a weld-in bung, and the block a group of fittings threads into is a manifold. Either can go on the same quote as the fittings. Fittings like these go into automotive and motorsport builds, energy and cleantech fluid systems and pump and fluid-handling equipment.

How does each end seal, and what goes on the print?

Each common end seals in a different place, which is why the print has to name it. A 37-degree AN or JIC end seals metal to metal, where the male cone meets the flare or the tapered gland (sources 1, 3). An ORB end has a straight thread and an O-ring, and it seals by compressing that O-ring into a taper at the mouth of the port (source 1). The straight threads themselves carry no seal and take no sealant (source 1). A straight thread with an O-ring pressed against a flat face is a different end, the straight-thread O-seal (source 1), so an ORB callout and a flat-face O-ring callout are not the same port.

Tapered pipe threads seal on the thread. NPT has a 60-degree thread form and tapers 1 in 16 on the diameter (sources 1, 5, 19), and it always needs a sealant (source 1); NPTF (Dryseal) is designed to seal without PTFE tape (source 5), so write NPT or NPTF and the size, because "pipe thread" alone is not a callout. Metric ports vary: an ISO 6149 port seals like ORB, with an O-ring in a taper, while a DIN 3852 Part 1 port seals with a gasket on a flat face (source 1).

For the straight-thread ends, the dash size is the tube OD in sixteenths of an inch (source 3), and a 37-degree end and an ORB port of the same dash size share one thread (source 1). That is how an AN-to-ORB adapter can carry the same thread on both ends and still need two different seals.

When the fitting carries a female ORB port, put the port standard on the print. Parker’s port table gives the thread, spot face and chamfer for each size, asks for the chamfer diameter to run concentric with the thread pitch diameter within 0.004 in FIM and to be free of lengthwise or spiral tool marks, and lists 90-durometer nitrile as the standard O-ring for hydraulic use (source 2). Position, perpendicularity and runout callouts are quoted from the print. An O-ring groove works by deforming the ring a set amount, and the most common failure is the ring extruding through the gap between the mating parts (source 6), so give the groove diameter, width and depth and the AS568 dash number of the ring (source 6). O-rings are not supplied with the parts.

SAE J1926/1, issued 17 January 2023, is the standard behind that port (source 20); it is sold by SAE and is not reproduced here. Name it on the print with the port dimensions.

Which material suits the fluid?

6061 aluminum is one of the most common general-purpose aluminum alloys (source 12). Anodizing raises its corrosion and wear resistance, and the common sulfuric-acid process takes dye (source 13), so a run can be clear, black or a color that matches the rest of an engine bay through anodizing. A finish called out on the print is quoted with the part. The coating grows half into and half out of the surface (source 13), so mark whether thread and seal dimensions apply before or after anodize, or which surfaces stay bare. Rush 1-2 weeks applies to machined parts with no secondary operations. Heat treat, grinding, EDM and finishing add time, and the quote gives the real date.

In stainless, 303 is the free-machining version of 304, with sulfur and phosphorus added (source 14). Carpenter lists fittings among its uses but does not recommend it for welding, because its high sulfur content may cause hot cracking, or for vessels containing gases or liquids under high pressures (source 18), so for a fitting that will be welded, or that holds gas or liquid under high pressure, name the use in the part description and the quote recommends another grade. 316 stainless adds molybdenum and is known as marine grade for its better resistance to chloride corrosion than 304 (source 14), so it is the grade to name for salt water or chloride-bearing fluids.

Titanium Grade 5 (Ti-6Al-4V) bar has a minimum yield strength of 120 ksi under ASTM B348 (source 17), and the alloy is about 1.65 times as dense as 6061 (4.43-4.51 against 2.70 g/cm³; sources 12, 16). If you are not sure which material fits, choose "Not sure - please advise" on the quote form and the quote recommends one. Other alloys and plastics quoted on request. Name the grade on the print.

Steel fittings are quoted in 12L14 or 1215. Both belong to the 12xx series, which is resulfurized and rephosphorized, and 12L14 is 1214 with lead added for machinability (source 14).

What should you send for a fitting quote?

Send the print, or a STEP file with notes. For a fitting, these are what the quote needs, and anything missing is listed on the quote.

Each end: the thread size and pitch, male or female, and the seal, such as a 37-degree flare, an ORB port with its standard, NPT or NPTF, a metric port with its standard, or a flat-face O-ring.

The body: overall length, the hex size across flats, the bore or orifice diameter with its tolerance if the fitting meters flow, and for a bulkhead the panel thickness and hole size.

Material and finish: the grade, or the fluid if you want a recommendation, and whether thread and seal dimensions apply before or after anodize.

The job: the fluid, its working pressure and temperature, and the quantity. Those steer the material recommendation. The quote does not state a pressure rating.

A STEP file with no drawing is quoted to a ±0.005 in general tolerance, or the one your notes name, so call out the threads and seals in the notes. A sketch or a new sample fitting can start the quote too; CAD from a sketch or sample is quoted as its own line, and reverse engineering explains how a part is remade from a sample. The sample ships back with the parts. A fully dimensioned 2D PDF is quoted without a CAD line. Lead time starts at order approval. Put your need date in the part description and the quote answers it. Ask for more than one quantity, such as 1, 25 and 100, and the quote shows each.

No C of C or material certifications ship with parts by default. If your PO needs them, say so before the quote. Inspection reports on critical dimensions aren’t included by default. If you need one, ask when you place the order.

Anything the print leaves out is listed on the quote, and how a 24-48 hour quote works covers what else comes back with it. Buyers in Michigan can start on CNC machining for Michigan companies, which has its own fittings section; parts ship anywhere in the US. The custom machined parts index lists fittings next to the flanges, bungs and manifolds that go with them.

Sources

All accessed 30 September 2026. Where a figure here differs from your print, the print governs.

1. Swagelok, "Thread and End Connection Identification Guide" (MS-13-77, Rev H), February 2025, swagelok.com/downloads/webcatalogs/en/ms-13-77.pdf (how 37-degree, ORB, O-seal, NPT, ISO 6149 and DIN 3852 Part 1 ends seal; sealants; threads by nominal size; the male and female 37-degree ends; the four facts that identify a thread).

2. Parker Hannifin, "SAE J1926-1 SAE Straight Thread O-ring Port (ISO 11926-1)", Catalog 4300, page U26, copy hosted by Goodyear Rubber Products, goodyearrubberproducts.com/files/parker/parkertubecatalog4300/parker%20tube%20catalog%204300examin1.page477.pdf (port threads, tube OD and O-ring sizes by dash size; chamfer concentricity and tool marks; 90-durometer nitrile).

3. Wikipedia, "AN thread": en.wikipedia.org/wiki/AN_thread (metal-to-metal 37-degree seal; dash sizes; thread class, shape and metals).

4. Wikipedia, "JIC fitting": en.wikipedia.org/wiki/JIC_fitting (dimensionally identical to AN, less exacting tolerances; 45-degree SAE flare and shared threads).

5. Wikipedia, "National pipe thread": en.wikipedia.org/wiki/National_pipe_thread (the 1 in 16 taper; NPTF seals without sealant).

6. Wikipedia, "O-ring": en.wikipedia.org/wiki/O-ring (groove and compression; extrusion as the common failure; AS568 dash numbers).

7. Peter Zelinski, "Understanding Swiss-Type Machining", Modern Machine Shop, published 26 June 2013, updated 14 July 2022: mmsonline.com/articles/understanding-swiss-type-machining (the tool cuts near the guide bushing, however long the part).

8. Wikipedia, "O-ring boss seal", last edited 3 August 2026: en.wikipedia.org/wiki/O-ring_boss_seal (the system can be confused with NPT; boss connectors should not be mixed with other connector types).

9. Wikipedia, "Cam and groove": en.wikipedia.org/wiki/Cam_and_groove (types A to F; MIL-C-27487 set dimensions and tolerances; A-A-59326 replaced it in 1998).

10. Colder Products Company, "An Introduction to Hose Barbed Fittings", white paper, 2007, copy hosted by Brookhaven National Laboratory, bnl.gov/esh/shsd/pdf/compressed_gas/barbedfittings-introduction.pdf (how a barb grips and seals; barb count; when to clamp).

11. Swagelok, "Stainless Steel Swagelok Tube Fitting, Bulkhead Union, 1/4 in. Tube OD", products.swagelok.com/en/c/straights/p/SS-400-61 (connection through a panel or enclosure).

12. Wikipedia, "6061 aluminium alloy": en.wikipedia.org/wiki/6061_aluminium_alloy (general-purpose use; density).

13. Wikipedia, "Anodizing": en.wikipedia.org/wiki/Anodizing (corrosion and wear resistance; dye; growth into and out of the surface).

14. Wikipedia, "SAE steel grades": en.wikipedia.org/wiki/SAE_steel_grades (303 and 304; 316, molybdenum and chlorides; the 12xx series as resulfurized and rephosphorized; 12L14 as 1214 with lead added).

15. Wikipedia, "Brass": en.wikipedia.org/wiki/Brass (C360 lead content; DZR brass).

16. Wikipedia, "Ti-6Al-4V": en.wikipedia.org/wiki/Ti-6Al-4V (density).

17. Performance Titanium Group, "ASTM B348 6AL-4V Grade 5", performancetitanium.com/astm-b348-6al-4v-grade-5/ (ASTM B348-25 Grade 5 bar minimum yield strength, 120 ksi).

18. Carpenter Technology, "CarTech 303 Stainless" technical datasheet, edition 29 May 2007: carpentertechnology.com/hubfs/7407324/Material%20Saftey%20Data%20Sheets/303.pdf (uses include fittings; welding; high-pressure vessels).

19. National Bureau of Standards (now NIST), Handbook H28 (1957), Part II, "Screw-Thread Standards for Federal Services", Section VII and Table VII.2 (American Standard taper pipe threads, NPT): nvlpubs.nist.gov (60-degree thread angle; taper of 1 in 16; pipe outside diameter, threads per inch and pitch diameter at the end of the pipe for each size; the current standard is ASME B1.20.1, source 5).

20. SAE International, "J1926/1_202301, Connections for General Use and Fluid Power - Ports and Stud Ends with ASME B1.1 Threads and O-Ring Sealing - Part 1: Threaded Port with O-Ring Seal in Truncated Housing", issued 17 January 2023: saemobilus.sae.org (title and issue date only; the standard is linked, not reproduced).