A4 Stainless Steel (ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80) is specified for marine, coastal and chemical applications. When unthreaded round spacers are specified in this grade, the dimensions remain per Trade series (plain bore spacer); the material determines corrosion behavior (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). Both are covered below with the size table.
Why Choose A4 Stainless Steel for Unthreaded Round Spacers
Specified for marine, coastal and chemical applications. For unthreaded round spacers, 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 |
Galvanic & Galling Considerations
For stainless unthreaded round spacers the compatibility question is galvanic rather than galling: joined to aluminum or galvanized steel in wet service, stainless drives corrosion of the less-noble metal. Isolate with a coating, sleeve or non-conductive washer where the joint sees moisture. Note also that stainless is softer than hardened carbon steel, so where the part carries a wear or shear duty, check the load against the grade before substituting.
Comparable Grades
For Unthreaded Round Spacers, 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 Unthreaded Round Spacers Available in A4 Stainless Steel
| Bore d1 (mm) | Outer diameter (mm) | Length L (mm) | Clears screw | Material | Finish | Tolerance on length |
|---|---|---|---|---|---|---|
| 3.2 | 6.0 | 5 | M3 | Aluminium | Plain | u00b10.2 mm |
| 3.2 | 6.0 | 10 | M3 | Aluminium | Plain | u00b10.2 mm |
| 3.2 | 6.0 | 20 | M3 | Nylon 6/6 | Natural | u00b10.3 mm |
| 4.2 | 8.0 | 10 | M4 | Brass | Nickel | u00b10.2 mm |
| 4.2 | 8.0 | 25 | M4 | Aluminium | Anodised | u00b10.2 mm |
| 5.2 | 10.0 | 15 | M5 | Aluminium | Anodised | u00b10.2 mm |
| 6.4 | 12.0 | 20 | M6 | Stainless | Passivated | u00b10.2 mm |
