A4 Stainless Steel (ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80) is specified for marine, coastal and chemical applications. When mirror screws with dome caps are specified in this grade, the dimensions remain per Trade series (mirror screw and cap); 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 Mirror Screws with Dome Caps
Specified for marine, coastal and chemical applications. For mirror screws with dome caps, 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
Two important notes for stainless mirror screws with dome caps: (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 Mirror Screws with Dome Caps, the alternative stainless grade is A2 (304). 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 Mirror Screws with Dome Caps Available in A4 Stainless Steel
| Screw size | Screw length (mm) | Cap thread | Cap diameter (mm) | Cap height (mm) | Cap finish | Screw drive | Material |
|---|---|---|---|---|---|---|---|
| No.8 / 4.2 mm | 32 | M4 | 12 | 5.0 | Polished chrome | PH2 | Steel, nickel plated |
| No.8 / 4.2 mm | 38 | M4 | 12 | 5.0 | Polished chrome | PH2 | Steel, nickel plated |
| No.10 / 5 mm | 38 | M4 | 14 | 6.0 | Polished chrome | PH2 | Steel, nickel plated |
| No.10 / 5 mm | 50 | M4 | 14 | 6.0 | Satin nickel | PH2 | A2 stainless |
| No.12 / 5.5 mm | 50 | M5 | 16 | 7.0 | Polished brass | PH2 | Brass |
