A4 Stainless Steel (ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80) is specified for marine, coastal and chemical applications. Specified on drilled-spanner security screws it determines the corrosion behaviour (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); the dimensions are ours rather than a standard's, and are listed in full below.
Why Choose A4 Stainless Steel for Drilled-Spanner Security Screws
Specified for marine, coastal and chemical applications. For drilled-spanner security screws, 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 Drilled-Spanner Security Screws in marine, coastal, swimming-pool or food-processing environments, A4 is the default selection.
Galvanic & Galling Considerations
Two important notes for stainless drilled-spanner security screws: (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 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 Drilled-Spanner Security Screws Available in A4 Stainless Steel
| Thread size | Head form | Head diameter (in) | Head height (in) | Length options (in) | Drive | Material |
|---|---|---|---|---|---|---|
| 4-40 undercut | flat 82-degree | 0.225 | 0.047 | 1/4 | two-hole drilled spanner | 18-8 stainless steel |
| 6-32 standard | flat 82-degree | 0.262 | 0.083 | 1/4~2 | two-hole drilled spanner | 18-8 stainless steel |
| 8-32 standard | flat 82-degree | 0.312 | 0.100 | 1/4~2 | two-hole drilled spanner | 18-8 stainless steel |
Dimensions are independent of the material: every size above is available in A4 Stainless Steel.
Custom manufacturing · Made to drawing
Need this screw in a grade that is not listed?
A4 Stainless Steel is one of the grades the catalog describes. Material and finish are usually what drives a special — a grade the standard part is not stocked in, or a coating chosen against a salt-spray figure instead of a default. Made by cold heading or warm forging.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
