Material specification page for key-locking threaded inserts in A4 Stainless Steel. Covers the grade designation (ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80), corrosion and magnetic behavior, comparable grades and their trade-offs, and the sizes available to Trade series (key-locking insert).
Why Choose A4 Stainless Steel for Key-Locking Threaded Inserts
Specified for marine, coastal and chemical applications. For key-locking threaded inserts, 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 Key-Locking Threaded Inserts in marine, coastal, swimming-pool or food-processing environments, A4 is the default selection.
Comparable Grades
For Key-Locking Threaded Inserts, the alternative stainless grade is A2 (304). The practical dividing line is chlorides: A2 (304) is fine until salt is involved, and A4 (316) exists for the cases where it is — coastal, marine and road-salt service. Neither reaches the strength of a plated class 8.8 or 10.9 fastener.
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 Key-Locking Threaded Inserts Available in A4 Stainless Steel
| Internal thread | External thread | Length L (mm) | Tapped hole required | Keys | Locking method | Material | Typical use |
|---|---|---|---|---|---|---|---|
| M4 | M8x1.0 | 8.0 | M8x1.0 | 4 | Driven keys broach parent | Carbon steel / 303 stainless | High-vibration repair |
| M5 | M10x1.25 | 10.0 | M10x1.25 | 4 | Driven keys broach parent | Carbon steel / 303 stainless | High-vibration repair |
| M6 | M12x1.25 | 12.0 | M12x1.25 | 4 | Driven keys broach parent | Carbon steel / 303 stainless | High-vibration repair |
| M8 | M14x1.25 | 14.0 | M14x1.25 | 4 | Driven keys broach parent | Carbon steel / 303 stainless | Aerospace, motorsport |
| M10 | M16x1.5 | 16.0 | M16x1.5 | 4 | Driven keys broach parent | Carbon steel / 303 stainless | Aerospace, motorsport |
| M12 | M20x1.5 | 20.0 | M20x1.5 | 4 | Driven keys broach parent | Carbon steel / 303 stainless | Aerospace, motorsport |
