For sems screws with captive spring washer in A4 Stainless Steel, the controlling selection factors are corrosion exposure, strength requirement and service temperature. The grade data for A4 Stainless Steel (ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80) is summarized below together with every size supplied.
Why Choose A4 Stainless Steel for SEMS Screws with Captive Spring Washer
Specified for marine, coastal and chemical applications. For sems screws with captive spring washer, 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 SEMS Screws with Captive Spring Washer in marine, coastal, swimming-pool or food-processing environments, A4 is the default selection.
Galvanic & Galling Considerations
Two important notes for stainless sems screws with captive spring washer: (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.
Using Stainless Fasteners in Aluminum
Stainless steel is more noble than aluminum, so in the presence of an electrolyte — rain, condensation, salt spray — the aluminum becomes the anode and corrodes at the joint. The effect is driven by the area ratio: a small stainless fastener in a large aluminum section is normally acceptable, while a large stainless fastener in thin aluminum is not. Where the joint is wet, isolate the two metals with a coated or nylon washer and a sealant, or specify an aluminum or coated fastener instead.
Sizes of SEMS Screws with Captive Spring Washer Available in A4 Stainless Steel
| Thread size | Pitch (mm) | Head diameter dk (mm) | Head height k (mm) | Washer outer diameter (mm) | Cross recess | Common length range (mm) | Reference standard |
|---|---|---|---|---|---|---|---|
| M3 | 0.5 | 5.6 | 2.4 | 6.2 | PH1 / PZ1 | 5~30 | DIN 6900-4 |
| M4 | 0.7 | 8.0 | 3.1 | 8.0 | PH2 / PZ2 | 6~40 | DIN 6900-4 |
| M5 | 0.8 | 9.5 | 3.7 | 10.0 | PH2 / PZ2 | 8~50 | DIN 6900-4 |
| M6 | 1.0 | 12.0 | 4.6 | 12.2 | PH3 / PZ3 | 8~60 | DIN 6900-4 |
| M8 | 1.25 | 16.0 | 6.0 | 15.4 | PH4 / PZ4 | 10~60 | DIN 6900-4 |
| M10 | 1.5 | 20.0 | 7.5 | 18.4 | PH4 / PZ4 | 12~60 | DIN 6900-4 |
