For self-drilling screws in A2 Stainless Steel, the controlling selection factors are corrosion exposure, strength requirement and service temperature. The grade data for A2 Stainless Steel (ISO 3506 group A2 (304 / 1.4301), commonly supplied A2-70) is summarized below together with every size supplied.
Why Choose A2 Stainless Steel for Self-Drilling Screws
The most common stainless group for indoor and general outdoor fasteners. For self-drilling screws, 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 |
Corrosion Behavior in Service
A2 (304) gives excellent atmospheric and most-water corrosion resistance and is the most common stainless for Self-Drilling Screws in indoor and general outdoor service. In chloride-bearing environments (marine air, road salt, swimming pools) consider stepping up to A4 (316).
Galvanic & Galling Considerations
Two important notes for stainless self-drilling 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.
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 Self-Drilling Screws Available in A2 Stainless Steel
| Size | Nominal diameter (mm) | Pitch (mm) | Head diameter dk (mm) | Head height k (mm) | Drill point capacity (mm) | Common length range (mm) | Reference standard | Notes |
|---|---|---|---|---|---|---|---|---|
| ST3.5 | 3.5 | 1.27 | 6.9 | 2.1 | 0.7~2.0 | 13~25 | DIN 7504 K/N | Tek self-drilling screw, drill flute point |
| ST3.9 | 3.9 | 1.29 | 7.5 | 2.3 | 0.7~2.5 | 13~32 | DIN 7504 K/N | Tek self-drilling screw, drill flute point |
| ST4.2 | 4.2 | 1.41 | 8.2 | 2.5 | 0.7~3.0 | 13~38 | DIN 7504 K/N | Tek self-drilling screw, drill flute point |
| ST4.8 | 4.8 | 1.59 | 9.5 | 2.9 | 0.7~4.0 | 16~50 | DIN 7504 K/N | Tek self-drilling screw, drill flute point |
| ST5.5 | 5.5 | 1.81 | 10.9 | 3.3 | 1.0~5.0 | 19~60 | DIN 7504 K/N | Tek self-drilling screw, drill flute point |
| ST6.3 | 6.3 | 1.81 | 12.5 | 3.8 | 1.0~6.0 | 19~80 | DIN 7504 K/N | Tek self-drilling screw, drill flute point |
