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 press-in and flare-in captive screws are specified in this grade, the dimensions remain per Trade series (panel captive screws); 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 Press-In and Flare-In Captive Screws
The most common stainless group for indoor and general outdoor fasteners. For press-in and flare-in captive 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 |
Galvanic & Galling Considerations
Two important notes for stainless press-in and flare-in captive 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 Press-In and Flare-In Captive Screws, the alternative stainless grade is A4 (316). 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
Expect the aluminum to corrode, not the fastener — stainless sits higher in the galvanic series, so the aluminum is the one that gives up material. A small fastener in a thick section spreads the loss over a large area and is usually fine; a large fastener in thin sheet concentrates it and is not. Keep water out of the joint, or isolate the two metals with a nylon or coated washer and a sealant.
Sizes of Press-In and Flare-In Captive Screws Available in A2 Stainless Steel
| Thread options | Press-in panel hole (mm) | Press-in ferrule (mm) | Flare-in ferrule (mm) | Drive options | Material options |
|---|---|---|---|---|---|
| M3 or 4-40 | 3.2 | 5.6 | 4.8 | Phillips/slot or Torx/slot | steel / stainless / aluminum |
| M3.5 or 6-32 | 3.7 | 6.4 | 5.4 | Phillips/slot or Torx/slot | steel / stainless / aluminum |
| M4 or 8-32 | 4.4 | 8.0 | 6.8 | Phillips/slot or Torx/slot | steel / stainless / aluminum |
| M5 or 10-32 | 5.2 | 8.0 | 6.8 | Phillips/slot or Torx/slot | steel / stainless / aluminum |
| M6 or 1/4-20 | 6.2 | 9.5 | 8.2 | Phillips/slot or Torx/slot | steel / stainless / aluminum |
