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Flat Washer Spec Table
Flat Washer Specifications — 75 sizes
KS B 1326ISO 7089JIS B 1256DIN 125
The most basic washer, placed under bolts/nuts to distribute bearing pressure and prevent surface damage.
Practical Notes
- Always use flat washers when bolt holes are 1–2mm larger than bolt diameter. Without washers, bolt heads can pull through.
- Use large washers (ISO 7093) on soft materials — aluminum, wood, plastic — to distribute bearing pressure.
Selection Guide
Essential for all bolt-nut assemblies. Distributes bearing pressure to prevent sinking, especially in aluminum, wood, and plastic. Always use with oversized holes or soft surfaces. Large washers (ISO 7093) suit pressure-sensitive materials.
Flat Washer
KSISOJISDINFlat Washer
15 sizesThe dimensions below are identical across KS B 1326 · ISO 7089 · JIS B 1256 · DIN 125.
| Nominal | d1 (Inner) | d2 (Outer) | h (Thick) | Type | Material |
|---|---|---|---|---|---|
| M3 | 3.2 | 7 | 0.5 | Flat Washer | - |
| M4 | 4.3 | 9 | 0.8 | Flat Washer | - |
| M5 | 5.3 | 10 | 1 | Flat Washer | - |
| M6 | 6.4 | 12 | 1.6 | Flat Washer | - |
| M8 | 8.4 | 16 | 1.6 | Flat Washer | - |
| M10 | 10.5 | 20 | 2 | Flat Washer | - |
| M12 | 13 | 24 | 2.5 | Flat Washer | - |
| M14 | 15 | 28 | 2.5 | Flat Washer | - |
| M16 | 17 | 30 | 3 | Flat Washer | - |
| M18 | 19 | 34 | 3 | Flat Washer | - |
| M20 | 21 | 37 | 3 | Flat Washer | - |
| M22 | 23 | 39 | 3 | Flat Washer | - |
| M24 | 25 | 44 | 4 | Flat Washer | - |
| M27 | 28 | 50 | 4 | Flat Washer | - |
| M30 | 31 | 56 | 4 | Flat Washer | - |
Key Features
- KS B 1326 / ISO 7089 (regular) / 7093 (large); distributes bearing pressure to prevent bolt sinking
- ID, OD, and thickness all standardized; auto-selected by bolt nominal size
- Corrosion class differentiated by zinc plating, stainless, or brass material
Key Applications
Basic washer for all bolt-nut fastening, wood bearing pressure distribution, paint surface protection, hole tolerance compensation
FAQ
How to choose flat washer ID and OD?
ID = bolt nominal diameter + 0.5–1mm clearance. OD is selected based on bearing pressure on the mating material. Use large washers (ISO 7093) for soft materials.