ASTM F3393 – Coatings Specification
ASTM F3393 is the unified standard for non-electrolytically applied zinc-flake coating systems on threaded fasteners. Consolidating and replacing three legacy standards—ASTM F1136, F2833, and F3019—this specification provides a streamlined framework for selecting coating performance based on corrosion resistance, thickness, and friction control. It applies to unified inch and metric fasteners with minimum diameters of 0.250 in. (6 mm) and requires a hexavalent chromium-free chemistry. For engineers and manufacturers, this standard is the primary reference for defining coating requirements during the ordering process to ensure mechanical integrity and consistent assembly performance.
Coating Properties
Coating performance under ASTM F3393 is defined by three primary classification codes: Corrosion Resistance (Table 1), Appearance (Table 2), and Friction Control (Table 3). When applying this specification, users must specify a combination of these codes to define the full coating system requirements.
- Corrosion Performance: Systems range from Grade A (240h) to Grade F (1200h) of salt spray resistance, with thickness and weight requirements increasing accordingly.
- Cathodic Protection: Coatings must prevent red corrosion for at least 72 hours when scratched to the base metal.
- Friction Control: To ensure predictable torque-tension relationships, the standard offers five distinct ranges for the average total coefficient of friction (µtot), ranging from 0.09 to 0.26.
- Application & Curing: Systems are typically applied via dip-spin or spray methods and cured at temperatures up to 671°F (355°C), which must not exceed the tempering temperature of quenched and tempered fasteners.
Refer to the tables below for the specific numeric and alpha codes required for ordering and quality verification.
| Minimum Corrosion Resistance, Minimum Coating Thickness, or Minimum Coating Weight | |||
|---|---|---|---|
| Classification Code | Minimum Corrosion Resistance | Minimum Coating Thickness | Minimum Coating Weight |
| A | 240h | 0.00016 in. (4 µm) | 0.0430 oz/ft² (13 g/m²) |
| B | 480h | 0.00020 in. (5 µm) | 0.0524 oz/ft² (16 g/m²) |
| C | 600h | 0.00025 in. (6 µm) | 0.0688 oz/ft² (21 g/m²) |
| D | 720h | 0.00030 in. (8 µm) | 0.0754 oz/ft² (23 g/m²) |
| E | 960h | 0.00050 in. (12 µm) | 0.0800 oz/ft² (24 g/m²) |
| F | 1200h | 0.00060 in. (15 µm) | 0.1180 oz/ft² (36 g/m²) |
| G | As Agreed Upon | As Agreed Upon | As Agreed Upon |
| Appearance | Classification Code | Appearance |
|---|---|
| 1 | Silver/Gray |
| 2 | Black |
| 3 | Other Colors (As Agreed Upon) |
| Average Coefficient of Total Friction Range and Test Program | |
|---|---|
| Classification Code | Average Coefficient of Total Friction (µtot)A |
| M | 0.09 ± 0.03 |
| N | 0.12 ± 0.03 |
| R | 0.15 ± 0.04 |
| S | 0.19 ± 0.05 |
| T | 0.26 ± 0.06 |
| W | As Agreed Upon |
| A The results for all tested samples must lie within the permissible range. | |