A4 Stainless Steel (ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80) is specified for marine, coastal and chemical applications. When turn-button fastener bases are specified in this grade, the dimensions remain per Trade series (turn-button fastener bases); 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 Turn-Button Fastener Bases
Specified for marine, coastal and chemical applications. For turn-button fastener bases, 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
For stainless turn-button fastener bases the compatibility question is galvanic rather than galling: joined to aluminum or galvanized steel in wet service, stainless drives corrosion of the less-noble metal. Isolate with a coating, sleeve or non-conductive washer where the joint sees moisture. Note also that stainless is softer than hardened carbon steel, so where the part carries a wear or shear duty, check the load against the grade before substituting.
Comparable Grades
For Turn-Button Fastener Bases, the alternative stainless grade is A2 (304). Choose A2 (304) for general use and A4 (316) wherever chlorides are present; the molybdenum in A4 is the whole difference. Remember that stainless is the corrosion answer, not the strength answer — for load, look at class 8.8 or 10.9 instead.
Using Stainless Fasteners in Aluminum
The galvanic couple here runs the wrong way: aluminum is the less noble metal, so it corrodes and the fastener does not. What governs the rate is the ratio of areas — a large anode and a small cathode is a tolerable combination, the reverse concentrates the attack into thin material around the hole. An isolating washer plus sealant breaks the circuit; where that is impractical, match the fastener to the substrate.
Sizes of Turn-Button Fastener Bases Available in A4 Stainless Steel
| Base form | Base dimensions (in) | Screw | Hole spacing (in) | Mounting holes | Material | Mating part |
|---|---|---|---|---|---|---|
| single-stud | 1-1/4 u00d7 1/2 u00d7 11/16 | No. 6 | 7/8 | two | nickel-plated brass | turn-button eyelet |
| double-stud | 1-1/4 u00d7 1/2 u00d7 7/8 | No. 8 | two | nickel-plated brass with stainless pin and spring | turn-button eyelet |
