A2 Stainless Steel (ISO 3506 group A2 (304 / 1.4301), commonly supplied A2-70) is the most common stainless group for indoor and general outdoor fasteners. When machine screws, inch (unc & unf) are specified in this grade, the dimensions remain per ASME B18.6.3; the material determines corrosion behavior (good general corrosion resistance) 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 A2 Stainless Steel for Machine Screws, Inch (UNC & UNF)
The most common stainless group for indoor and general outdoor fasteners. For machine screws, inch (unc & unf), this matters when good general corrosion resistance is the primary requirement.
Mechanical & Physical Properties
| Grade designation | ISO 3506 group A2 (304 / 1.4301), commonly supplied A2-70 |
|---|---|
| Magnetic response | Largely non-magnetic |
| Service temperature | approx. -200 °C to +400 °C, subject to the property class and the joint |
| Corrosion characteristic | Good general corrosion resistance |
Galvanic & Galling Considerations
Two important notes for stainless machine screws, inch (unc & unf): (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 Machine Screws, Inch (UNC & UNF), the alternative stainless grade is A4 (316). 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 Machine Screws, Inch (UNC & UNF) Available in A2 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 A2 Stainless Steel.
Custom manufacturing · Made to drawing
Need this screw in a grade that is not listed?
A2 Stainless Steel is one of the grades the catalog describes. Head form and drive can be specified to the assembly rather than to a standard: a larger bearing face, a security drive, or a socket sized for the tool already on the bench. Made by cold heading or warm forging.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
