Material specification page for machine screws, inch (unc & unf) 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 B18.6.3.
Why Choose A4 Stainless Steel for Machine Screws, Inch (UNC & UNF)
Specified for marine, coastal and chemical applications. For machine screws, inch (unc & unf), 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 Screws, Inch (UNC & UNF) in marine, coastal, swimming-pool or food-processing environments, A4 is the default selection.
Comparable Grades
For Machine Screws, Inch (UNC & UNF), the alternative stainless grade is A2 (304). A2 (304) covers general indoor and outdoor service. A4 (316) adds molybdenum, which is what buys the chloride resistance for marine and de-icing-salt exposure. Where strength matters more than corrosion, plated alloy steel in class 8.8 or 10.9 is the swap to make.
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 Machine Screws, Inch (UNC & UNF) Available in A4 Stainless Steel
| Size | UNC threads per inch | UNF threads per inch | Major diameter (in) | Pan head diameter (in) | Pan head height (in) | Drive | Reference standard |
|---|---|---|---|---|---|---|---|
| #2 | 56 | 64 | 0.086 | 0.167 | 0.053 | PH1 | ASME B18.6.3 |
| #4 | 40 | 48 | 0.112 | 0.219 | 0.068 | PH1 | ASME B18.6.3 |
| #6 | 32 | 40 | 0.138 | 0.270 | 0.082 | PH2 | ASME B18.6.3 |
| #8 | 32 | 36 | 0.164 | 0.322 | 0.096 | PH2 | ASME B18.6.3 |
| #10 | 24 | 32 | 0.190 | 0.373 | 0.110 | PH2 | ASME B18.6.3 |
| 1/4" | 20 | 28 | 0.250 | 0.492 | 0.144 | PH2 / PH3 | ASME B18.6.3 |
Dimensions are independent of the material: every size above is available in A4 Stainless Steel.
Custom manufacturing · Made to drawing
Need this screw in a grade that is not listed?
A4 Stainless Steel is one of the grades the catalog describes. Where the standard stops, the drawing takes over: fine pitches, left-hand threads, partial threading, and property classes above the catalogued grade where material and heat treatment allow. Made by cold heading or warm forging.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
