Large-Diameter Lockbolt Assemblies (BS 7805-2) manufactured in A4 Stainless Steel (ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80) are dimensioned to BS 7805 Part 2:1997. The sections below give the mechanical and physical properties of the grade, its behavior in corrosive and elevated-temperature service, and the full size table.
Why Choose A4 Stainless Steel for Large-Diameter Lockbolt Assemblies (BS 7805-2)
Specified for marine, coastal and chemical applications. For large-diameter lockbolt assemblies (bs 7805-2), 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 Large-Diameter Lockbolt Assemblies (BS 7805-2) in marine, coastal, swimming-pool or food-processing environments, A4 is the default selection.
Comparable Grades
For Large-Diameter Lockbolt Assemblies (BS 7805-2), 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
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 Large-Diameter Lockbolt Assemblies (BS 7805-2) Available in A4 Stainless Steel
| Nominal diameter (mm) | Pin head styles | Collar styles | Strength grade | Assembly | Material options | Reference standard |
|---|---|---|---|---|---|---|
| 12.7 | round / truss / countersunk / threaded-head | standard / flanged / low-profile | 8.8 | pin + collar | steel / stainless steel / aluminum alloy | BS 7805 Part 2:1997 |
| 15.9 | round / truss / countersunk / threaded-head | standard / flanged / low-profile | 8.8 | pin + collar | steel / stainless steel / aluminum alloy | BS 7805 Part 2:1997 |
| 19.1 | round / truss / countersunk / threaded-head | standard / flanged / low-profile | 8.8 | pin + collar | steel / stainless steel / aluminum alloy | BS 7805 Part 2:1997 |
| 22.2 | round / truss / countersunk / threaded-head | standard / flanged / low-profile | 8.8 | pin + collar | steel / stainless steel / aluminum alloy | BS 7805 Part 2:1997 |
| 25.4 | round / truss / countersunk / threaded-head | standard / flanged / low-profile | 8.8 | pin + collar | steel / stainless steel / aluminum alloy | BS 7805 Part 2:1997 |
| 28.6 | round / truss / countersunk / threaded-head | standard / flanged / low-profile | 8.8 | pin + collar | steel / stainless steel / aluminum alloy | BS 7805 Part 2:1997 |
| 31.8 | round / truss / countersunk / threaded-head | standard / flanged / low-profile | 8.8 | pin + collar | steel / stainless steel / aluminum alloy | BS 7805 Part 2:1997 |
| 34.9 | round / truss / countersunk / threaded-head | standard / flanged / low-profile | 8.8 | pin + collar | steel / stainless steel / aluminum alloy | BS 7805 Part 2:1997 |
