A4 Stainless Steel (ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80) is specified for marine, coastal and chemical applications. When npt pipe thread fittings are specified in this grade, the dimensions remain per ASME B1.20.1; the material determines corrosion behavior (superior, including marine and chloride environments) and the service temperature range (approx. -200 °C to +400 °C, subject to the property class and the joint). Both are covered below with the size table.
Why Choose A4 Stainless Steel for NPT Pipe Thread Fittings
Specified for marine, coastal and chemical applications. For npt pipe thread fittings, this matters when superior, including marine and chloride environments is the primary requirement.
Mechanical & Physical Properties
| Grade designation | ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80 |
|---|---|
| Magnetic response | Largely non-magnetic |
| Service temperature | approx. -200 °C to +400 °C, subject to the property class and the joint |
| Corrosion characteristic | Superior, including marine and chloride environments |
Galvanic & Galling Considerations
Two important notes for stainless npt pipe thread fittings: (1) stainless can gall on stainless threads under load — use a thread lubricant or anti-galling compound, especially for M6 and below; (2) when joined to aluminum or galvanized steel, stainless can drive galvanic corrosion of the less-noble metal in wet service — isolate with a coating or sleeve where appropriate.
Comparable Grades
For NPT Pipe Thread Fittings, the alternative stainless grade is A2 (304). Choose A2 (304) for general use and A4 (316) wherever chlorides are present; the molybdenum in A4 is the whole difference. Remember that stainless is the corrosion answer, not the strength answer — for load, look at class 8.8 or 10.9 instead.
Using Stainless Fasteners in Aluminum
The galvanic couple here runs the wrong way: aluminum is the less noble metal, so it corrodes and the fastener does not. What governs the rate is the ratio of areas — a large anode and a small cathode is a tolerable combination, the reverse concentrates the attack into thin material around the hole. An isolating washer plus sealant breaks the circuit; where that is impractical, match the fastener to the substrate.
Sizes of NPT Pipe Thread Fittings Available in A4 Stainless Steel
| Size | Nominal size (in) | Major diameter (mm) | Pitch (mm) | Threads per inch (TPI) | Taper | Reference standard | Notes |
|---|---|---|---|---|---|---|---|
| 1/16 NPT | 1/16 | 7.938 | 0.941 | 27 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 1/8 NPT | 1/8 | 10.287 | 0.941 | 27 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 1/4 NPT | 1/4 | 13.716 | 1.411 | 18 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 3/8 NPT | 3/8 | 17.145 | 1.411 | 18 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 1/2 NPT | 1/2 | 21.336 | 1.814 | 14 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 3/4 NPT | 3/4 | 26.67 | 1.814 | 14 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 1 NPT | 1 | 33.401 | 2.209 | 11.5 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 1-1/4 NPT | 1-1/4 | 42.164 | 2.209 | 11.5 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 1-1/2 NPT | 1-1/2 | 48.26 | 2.209 | 11.5 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 2 NPT | 2 | 60.325 | 2.209 | 11.5 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 2-1/2 NPT | 2-1/2 | 73.025 | 3.175 | 8 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 3 NPT | 3 | 88.9 | 3.175 | 8 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 3-1/2 NPT | 3-1/2 | 101.6 | 3.175 | 8 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 4 NPT | 4 | 114.3 | 3.175 | 8 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 5 NPT | 5 | 141.3 | 3.175 | 8 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 6 NPT | 6 | 168.275 | 3.175 | 8 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
Dimensions are independent of the material: every size above is available in A4 Stainless Steel.
Custom manufacturing · Made to drawing
Need this pipe & pneumatic fitting in a grade that is not listed?
A4 Stainless Steel is one of the grades the catalog describes. Dimensions, material, finish and form are specified from the drawing — a pipe & pneumatic fitting outside the standard range is a variation on existing tooling rather than a new design.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
