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 thin castle nuts (din 937) are specified in this grade, the dimensions remain per DIN 937; 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 Thin Castle Nuts (DIN 937)
The most common stainless group for indoor and general outdoor fasteners. For thin castle nuts (din 937), 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 thin castle nuts (din 937): (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 Thin Castle Nuts (DIN 937), 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
Stainless steel is more noble than aluminum, so with an electrolyte present — rain, condensation, salt spray — the aluminum becomes the anode and corrodes at the joint. Area ratio decides how bad it gets: a small stainless fastener in a large aluminum section is normally acceptable, a large stainless fastener in thin aluminum is not. Where the joint gets wet, isolate the metals with a coated or nylon washer and a sealant, or specify an aluminum or coated fastener instead.
Sizes of Thin Castle Nuts (DIN 937) Available in A2 Stainless Steel
| Thread size | Pitch (mm) | Width across flats s (mm) | Total height m (mm) | Height vs DIN 935 | Slot width n (mm) | Split pin size | Reference standard |
|---|---|---|---|---|---|---|---|
| M10 | 1.5 | 17.0 | 8.0 | approx. 70% | 2.8 | 2.5 x 30 | DIN 937 |
| M12 | 1.75 | 19.0 | 10.0 | approx. 71% | 3.5 | 3.2 x 36 | DIN 937 |
| M16 | 2.0 | 24.0 | 13.0 | approx. 76% | 4.5 | 4 x 40 | DIN 937 |
| M20 | 2.5 | 30.0 | 16.0 | approx. 80% | 4.5 | 4 x 50 | DIN 937 |
| M24 | 3.0 | 36.0 | 19.0 | approx. 79% | 5.5 | 5 x 63 | DIN 937 |
