A4 Stainless Steel (ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80) is specified for marine, coastal and chemical applications. Specified on thumb nuts (type a) 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 Thumb Nuts (Type A)
Specified for marine, coastal and chemical applications. For thumb nuts (type a), 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 Thumb Nuts (Type A) in marine, coastal, swimming-pool or food-processing environments, A4 is the default selection.
Galvanic & Galling Considerations
Two important notes for stainless thumb nuts (type a): (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 Thumb Nuts (Type A) Available in A4 Stainless Steel
| Thread size | Blade width B (mm) | Blade height H (mm) | Base diameter (mm) | Thickness (mm) | Reference standard |
|---|---|---|---|---|---|
| No.6-32 | 15.9 | 9.5 | 7.9 | 1.5 | Industry standard |
| No.8-32 | 17.5 | 10.3 | 9.5 | 1.5 | Industry standard |
| No.10-24 | 19.1 | 11.1 | 10.3 | 1.9 | Industry standard |
| 1/4"-20 | 22.2 | 12.7 | 12.7 | 1.9 | Industry standard |
| 5/16"-18 | 25.4 | 14.3 | 14.3 | 2.4 | Industry standard |
| 3/8"-16 | 28.6 | 15.9 | 15.9 | 2.4 | Industry standard |
Dimensions are independent of the material: every size above is available in A4 Stainless Steel.
Custom manufacturing · Made to drawing
Need this nut in a grade that is not listed?
A4 Stainless Steel is one of the grades the catalog describes. Dimensions, material, finish and form are specified from the drawing — a nut outside the standard range is a variation on existing tooling rather than a new design. Made by cold heading or tapping.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
