Material specification page for castle nuts (din 935) in A4 Stainless Steel. Covers the grade designation (ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80), corrosion and magnetic behavior, comparable grades and their trade-offs, and the sizes available to DIN 935.
Why Choose A4 Stainless Steel for Castle Nuts (DIN 935)
Specified for marine, coastal and chemical applications. For castle nuts (din 935), 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 |
Corrosion Behavior in Service
A4 (316) adds 2–3% molybdenum to the A2 (304) composition, which dramatically improves resistance to chloride-pitting corrosion. For Castle Nuts (DIN 935) in marine, coastal, swimming-pool or food-processing environments, A4 is the default selection.
Comparable Grades
For Castle Nuts (DIN 935), the alternative stainless grade is A2 (304). The practical dividing line is chlorides: A2 (304) is fine until salt is involved, and A4 (316) exists for the cases where it is — coastal, marine and road-salt service. Neither reaches the strength of a plated class 8.8 or 10.9 fastener.
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 Castle Nuts (DIN 935) Available in A4 Stainless Steel
| Thread size | Pitch (mm) | Width across flats s (mm) | Total height m (mm) | Slot width n (mm) | Slot depth (mm) | Split pin size | Reference standard |
|---|---|---|---|---|---|---|---|
| M8 | 1.25 | 13.0 | 9.5 | 2.5 | 3.5 | 2 x 25 | DIN 935 |
| M10 | 1.5 | 17.0 | 11.5 | 2.8 | 4.0 | 2.5 x 30 | DIN 935 |
| M12 | 1.75 | 19.0 | 14.0 | 3.5 | 5.5 | 3.2 x 36 | DIN 935 |
| M16 | 2.0 | 24.0 | 17.0 | 4.5 | 6.0 | 4 x 40 | DIN 935 |
| M20 | 2.5 | 30.0 | 20.0 | 4.5 | 6.0 | 4 x 50 | DIN 935 |
| M24 | 3.0 | 36.0 | 24.0 | 5.5 | 8.0 | 5 x 63 | DIN 935 |
