A4 Stainless Steel (ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80) is specified for marine, coastal and chemical applications. When phillips countersunk screws are specified in this grade, the dimensions remain per ISO 7046 / DIN 965; 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 Phillips Countersunk Screws
Specified for marine, coastal and chemical applications. For phillips countersunk screws, 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 phillips countersunk screws: (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 Phillips Countersunk Screws, the alternative stainless grade is A2 (304). A2 (304) suits general indoor and outdoor service; A4 (316) adds molybdenum for marine and chloride environments. Where higher strength matters more than corrosion, switch to plated alloy-steel class 8.8 or 10.9.
Using Stainless Fasteners in Aluminum
Stainless steel is more noble than aluminum, so in the presence of an electrolyte — rain, condensation, salt spray — the aluminum becomes the anode and corrodes at the joint. The effect is driven by the area ratio: a small stainless fastener in a large aluminum section is normally acceptable, while a large stainless fastener in thin aluminum is not. Where the joint is wet, isolate the two metals with a coated or nylon washer and a sealant, or specify an aluminum or coated fastener instead.
Sizes of Phillips Countersunk Screws Available in A4 Stainless Steel
| Size | Pitch (mm) | Head diameter dk (mm) | Head height k (mm) | Cross recess | Countersink angle (deg) | Reference standard |
|---|---|---|---|---|---|---|
| M1.6 | 0.35 | 3.0 | 0.96 | PH0 | 90 | ISO 7046 / DIN 965 |
| M2 | 0.4 | 3.8 | 1.2 | PH1 | 90 | ISO 7046 / DIN 965 |
| M2.5 | 0.45 | 4.7 | 1.5 | PH1 | 90 | ISO 7046 / DIN 965 |
| M3 | 0.5 | 5.6 | 1.65 | PH1 | 90 | ISO 7046 / DIN 965 |
| M3.5 | 0.6 | 6.5 | 1.93 | PH2 | 90 | ISO 7046 / DIN 965 |
| M4 | 0.7 | 7.5 | 2.2 | PH2 | 90 | ISO 7046 / DIN 965 |
| M5 | 0.8 | 9.2 | 2.5 | PH2 | 90 | ISO 7046 / DIN 965 |
| M6 | 1.0 | 11.0 | 3.0 | PH3 | 90 | ISO 7046 / DIN 965 |
| M8 | 1.25 | 14.5 | 4.0 | PH3 | 90 | ISO 7046 / DIN 965 |
| M10 | 1.5 | 18.0 | 5.0 | PH4 | 90 | ISO 7046 / DIN 965 |
