Material specification page for machine screw nuts, unc (hex and square) in A4 Stainless Steel. Covers the grade designation (ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80), corrosion and magnetic behavior, comparable grades and their trade-offs, and the sizes available to ASME B18.2.2.
Why Choose A4 Stainless Steel for Machine Screw Nuts, UNC (Hex and Square)
Specified for marine, coastal and chemical applications. For machine screw nuts, unc (hex and square), 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 |
Corrosion Behavior in Service
A4 (316) adds 2–3% molybdenum to the A2 (304) composition, which dramatically improves resistance to chloride-pitting corrosion. For Machine Screw Nuts, UNC (Hex and Square) in marine, coastal, swimming-pool or food-processing environments, A4 is the default selection.
Comparable Grades
For Machine Screw Nuts, UNC (Hex and Square), 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
Stainless steel is more noble than aluminum, so with an electrolyte present — rain, condensation, salt spray — the aluminum becomes the anode and corrodes at the joint. Area ratio decides how bad it gets: a small stainless fastener in a large aluminum section is normally acceptable, a large stainless fastener in thin aluminum is not. Where the joint gets wet, isolate the metals with a coated or nylon washer and a sealant, or specify an aluminum or coated fastener instead.
Sizes of Machine Screw Nuts, UNC (Hex and Square) Available in A4 Stainless Steel
| Size | Type | Pitch P (mm) | da (mm) | Width across corners e (mm) | Nut height m (mm) | Width across flats s (mm) | Reference standard |
|---|---|---|---|---|---|---|---|
| #0 | Hex Machine screw nuts | 0.318 | 1.714 | 4.458 | 1.181 | 3.886 | ASME B18.2.2 |
| #0 | Square machine screw nuts | 0.318 | 1.714 | 4.458 | 1.181 | 3.886 | ASME B18.2.2 |
| #1 | Hex Machine screw nuts | 0.397 | 2.086 | 4.458 | 1.181 | 3.886 | ASME B18.2.2 |
| #1 | Square machine screw nuts | 0.397 | 2.086 | 4.458 | 1.181 | 3.886 | ASME B18.2.2 |
| #2 | Hex Machine screw nuts | 0.454 | 2.457 | 5.359 | 1.562 | 4.674 | ASME B18.2.2 |
| #2 | Square machine screw nuts | 0.454 | 2.457 | 5.359 | 1.562 | 4.674 | ASME B18.2.2 |
| #3 | Hex Machine screw nuts | 0.529 | 2.829 | 5.359 | 1.562 | 4.674 | ASME B18.2.2 |
| #3 | Square machine screw nuts | 0.529 | 2.829 | 5.359 | 1.562 | 4.674 | ASME B18.2.2 |
| #4 | Hex Machine screw nuts | 0.635 | 3.2 | 7.163 | 2.349 | 6.236 | ASME B18.2.2 |
| #4 | Square machine screw nuts | 0.635 | 3.2 | 7.163 | 2.349 | 6.236 | ASME B18.2.2 |
| #5 | Hex Machine screw nuts | 0.635 | 3.572 | 8.954 | 2.743 | 7.798 | ASME B18.2.2 |
| #5 | Square machine screw nuts | 0.635 | 3.572 | 8.954 | 2.743 | 7.798 | ASME B18.2.2 |
| #6 | Hex Machine screw nuts | 0.794 | 3.943 | 8.954 | 2.743 | 7.798 | ASME B18.2.2 |
| #6 | Square machine screw nuts | 0.794 | 3.943 | 8.954 | 2.743 | 7.798 | ASME B18.2.2 |
| #8 | Hex Machine screw nuts | 0.794 | 4.686 | 9.842 | 3.137 | 8.585 | ASME B18.2.2 |
| #8 | Square machine screw nuts | 0.794 | 4.686 | 9.842 | 3.137 | 8.585 | ASME B18.2.2 |
| #10 | Hex Machine screw nuts | 1.058 | 5.429 | 10.744 | 3.137 | 9.36 | ASME B18.2.2 |
| #10 | Square machine screw nuts | 1.058 | 5.429 | 10.744 | 3.137 | 9.36 | ASME B18.2.2 |
| #12 | Hex Machine screw nuts | 1.058 | 6.172 | 12.535 | 3.924 | 10.935 | ASME B18.2.2 |
| #12 | Square machine screw nuts | 1.058 | 6.172 | 12.535 | 3.924 | 10.935 | ASME B18.2.2 |
| 1/4" | Hex Machine screw nuts | 1.27 | 7.144 | 12.535 | 4.712 | 10.935 | ASME B18.2.2 |
| 1/4" | Square machine screw nuts | 1.27 | 7.144 | 12.535 | 4.712 | 10.935 | ASME B18.2.2 |
| 5/16" | Hex Machine screw nuts | 1.411 | 8.915 | 16.142 | 5.499 | 14.059 | ASME B18.2.2 |
| 5/16" | Square machine screw nuts | 1.411 | 8.915 | 16.142 | 5.499 | 14.059 | ASME B18.2.2 |
| 3/8" | Hex Machine screw nuts | 1.587 | 10.716 | 17.958 | 6.299 | 15.646 | ASME B18.2.2 |
| 3/8" | Square machine screw nuts | 1.587 | 10.716 | 17.958 | 6.299 | 15.646 | ASME B18.2.2 |
Dimensions are independent of the material: every size above is available in A4 Stainless Steel.
Custom manufacturing · Made to drawing
Need this nut in a grade that is not listed?
A4 Stainless Steel is one of the grades the catalog describes. Locking method is specifiable independently of the rest: nylon insert, all-metal deformed thread, serrated flange, or none. Made by cold heading or tapping.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
