Flat Washer (BS 4320)
BS 4320 Flat washers are more slender than the heavier obligation structure A sort washers. They are produced using tempered steel grade 304 (A2) for protection from erosion, and adjust to BS 4320 guidelines.
Washers give a smooth surface to the nut or screw to bear on, making it doubtful to release because of a lopsided securing surface.
The fundamental reason for a washer is to disseminate the heap under a screw head or the nut face.
Hardened steel doesn’t promptly consume, rust or stain with water as common steel does. Notwithstanding, it isn’t completely stain-confirmation in low-oxygen, high saltiness, or helpless air-dissemination conditions. There are various grades and surface completions of hardened steel to suit the climate the combination should persevere. Treated steel is utilized where both the properties or steel and consumption obstruction are required.
- BS 4320
- Quality: 100 HV
- Coating: Self, Black, Bright Zinc, Hot Dip Galvanized
- Thread: METRIC
BS 4320
Technical Specification for BS 4320 Flat Washer
| Nominal Washer Size | Inside Diameter (ID) | Outside Diameter (OD) | Thickness (s) | |||||||
| Min. | Max. | Min. | Max. | FORM A | FORM B | |||||
| Nom. | Max. | Min. | Nom. | Max. | Min. | |||||
| M3 | 3.2 | 3.4 | 6.7 | 7 | 0.5 | 0.6 | 0.4 | – | – | – |
| M4 | 4.3 | 4.5 | 8.7 | 9 | 0.8 | 0.9 | 0.7 | – | – | – |
| M5 | 5.3 | 5.5 | 9.7 | 10 | 1 | 1.1 | 0.9 | – | – | – |
| M6 | 6.4 | 6.7 | 12.1 | 12.5 | 1.6 | 1.8 | 1.4 | 0.8 | 0.9 | 0.7 |
| M8 | 8.4 | 8.7 | 16.6 | 17 | 1.6 | 1.8 | 1.4 | 1 | 1.1 | 0.9 |
| M10 | 10.5 | 10.9 | 20.5 | 21 | 2 | 2.2 | 1.8 | 1.25 | 1.45 | 1.05 |
| M12 | 13 | 13.4 | 23.5 | 24 | 2.5 | 2.7 | 2.3 | 1.6 | 1.8 | 1.4 |
| (M14) | 15 | 15.4 | 27.5 | 28 | 2.5 | 2.7 | 2.3 | 1.6 | 1.8 | 1.4 |
| M16 | 17 | 17.4 | 29.5 | 30 | 3 | 3.3 | 2.7 | 2 | 2.2 | 1.8 |
| (M18) | 19 | 19.5 | 33.2 | 34 | 3 | 3.3 | 2.7 | 2 | 2.2 | 1.8 |
| M20 | 21 | 21.5 | 36.2 | 37 | 3 | 3.3 | 2.7 | 2 | 2.2 | 1.8 |
| (M22) | 23 | 23.5 | 38.2 | 39 | 3 | 3.3 | 2.7 | 2 | 2.2 | 1.8 |
| M24 | 25 | 25.5 | 43.2 | 44 | 4 | 4.3 | 3.7 | 2.5 | 2.7 | 2.3 |
| (M27) | 28 | 28.5 | 49.2 | 50 | 4 | 4.3 | 3.7 | 2.5 | 2.7 | 2.3 |
| M30 | 31 | 31.6 | 55 | 56 | 4 | 4.3 | 3.7 | 2.5 | 2.7 | 2.3 |
| (M33) | 34 | 34.6 | 59 | 60 | 5 | 5.6 | 4.4 | 3 | 3.3 | 2.7 |
| M36 | 37 | 37.6 | 65 | 66 | 5 | 5.6 | 4.4 | 3 | 3.3 | 2.7 |
| (M39) | 40 | 40.6 | 71 | 72 | 6 | 6.6 | 5.4 | 3 | 3.3 | 2.7 |
| Nominal Washer Size | Inside Diameter (ID) | Outside Diameter (OD) | Thickness (s) | |||||||
| Min. | Max. | Min. | Max. | FORM C | FORM D | |||||
| Nom. | Max. | Min. | Nom. | Max. | Min. | |||||
| M4 | 4.3 | 4.5 | 9.7 | 10 | 0.8 | 0.9 | 0.7 | – | – | – |
| M5 | 5.3 | 5.5 | 12.1 | 12.5 | 1 | 1.1 | 0.9 | – | – | – |
| M6 | 6.4 | 6.7 | 13.6 | 14 | 1.6 | 1.8 | 1.4 | 0.8 | 0.9 | 0.7 |
| M8 | 8.4 | 8.7 | 20.5 | 21 | 1.6 | 1.8 | 1.4 | 1 | 1.1 | 0.9 |
| M10 | 10.5 | 10.9 | 23.5 | 24 | 2 | 2.2 | 1.8 | 1.25 | 1.45 | 1.05 |
| M12 | 13 | 13.4 | 27.5 | 28 | 2.5 | 2.7 | 2.3 | 1.6 | 1.8 | 1.4 |
| (M14) | 15 | 15.4 | 29.5 | 30 | 2.5 | 2.7 | 2.3 | 1.6 | 1.8 | 1.4 |
| M16 | 17 | 17.4 | 33.2 | 34 | 3 | 3.3 | 2.7 | 2 | 2.2 | 1.8 |
| (M18) | 19 | 19.5 | 36.2 | 37 | 3 | 3.3 | 2.7 | 2 | 2.2 | 1.8 |
| M20 | 21 | 21.5 | 38.2 | 39 | 3 | 3.3 | 2.7 | 2 | 2.2 | 1.8 |
| (M22) | 23 | 23.5 | 43.2 | 44 | 3 | 3.3 | 2.7 | 2 | 2.2 | 1.8 |
| M24 | 25 | 25.5 | 49.2 | 50 | 4 | 4.3 | 3.7 | 2.5 | 2.7 | 2.3 |
| (M27) | 28 | 28.5 | 55 | 56 | 4 | 4.3 | 3.7 | 2.5 | 2.7 | 2.3 |
| M30 | 31 | 31.6 | 59 | 60 | 4 | 4.3 | 3.7 | 2.5 | 2.7 | 2.3 |
| (M33) | 31 | 31.6 | 65 | 66 | 5 | 5.6 | 4.4 | 3 | 3.3 | 2.7 |
| M36 | 37 | 37.6 | 71 | 72 | 5 | 5.6 | 4.4 | 3 | 3.3 | 2.7 |
| (M39) | 40 | 40.6 | 76 | 77 | 6 | 6.6 | 5.4 | 3 | 3.3 | 2.7 |
| Nominal Washer Size | Inside Diameter (ID) | Outside Diameter (OD) | Thickness (s) | ||||
| Min. | Max. | Min. | Max. | FORM F | |||
| Nom. | Max. | Min. | |||||
| M8 | 9 | 9.4 | 20.2 | 21 | 1.6 | 1.9 | 1.3 |
| M10 | 11 | 11.5 | 23.2 | 24 | 2 | 2.3 | 1.7 |
| M12 | 14 | 14.5 | 27.2 | 28 | 2.5 | 2.8 | 2.2 |
| (M14) | 16 | 16.5 | 29.2 | 30 | 2.5 | 2.8 | 2.2 |
| M16 | 18 | 18.5 | 32.8 | 34 | 3 | 3.6 | 2.4 |
| (M18) | 20 | 20.6 | 35.8 | 37 | 3 | 3.6 | 2.4 |
| M20 | 22 | 22.6 | 37.8 | 39 | 3 | 3.6 | 2.4 |
| (M22) | 24 | 24.6 | 42.8 | 44 | 3 | 3.6 | 2.4 |
| M24 | 26 | 26.6 | 48.8 | 50 | 4 | 4.6 | 3.4 |
| (M27) | 30 | 30.6 | 54.5 | 56 | 4 | 4.6 | 3.4 |
| M30 | 33 | 33.8 | 58.5 | 60 | 4 | 4.6 | 3.4 |
| (M33) | 36 | 36.8 | 64.5 | 66 | 5 | 6 | 4 |
| M36 | 39 | 39.8 | 70.5 | 72 | 5 | 6 | 4 |
| (M39) | 42 | 42.8 | 75.5 | 77 | 6 | 7 | 5 |
| Nominal Washer Size | Inside Diameter (ID) | Outside Diameter (OD) | Thickness (s) | ||||
| Min. | Max. | Min. | Max. | FORM G | |||
| Nom. | Max. | Min. | |||||
| M5 | 5.5 | 5.8 | 14.2 | 15 | 1.6 | 1.9 | 1.3 |
| M6 | 6.6 | 7 | 17.2 | 18 | 2 | 2.3 | 1.7 |
| M8 | 9 | 9.4 | 23.2 | 24 | 2 | 2.3 | 1.7 |
| M10 | 11 | 11.5 | 29.2 | 30 | 2.5 | 2.8 | 2.2 |
| M12 | 14 | 14.5 | 34.8 | 36 | 3 | 3.6 | 2.4 |
| (M14) | 16 | 16.5 | 40.8 | 42 | 3 | 3.6 | 2.4 |
| M16 | 18 | 18.5 | 46.8 | 48 | 4 | 4.6 | 3.8 |
| (M18) | 20 | 20.6 | 52.5 | 54 | 4 | 4.6 | 3.4 |
| M20 | 22 | 22.6 | 58.5 | 60 | 5 | 6 | 4 |
| (M22) | 24 | 24.6 | 64.5 | 66 | 5 | 6 | 4 |
| M24 | 26 | 26.6 | 70.5 | 72 | 6 | 7 | 5 |
| (M27) | 30 | 30.6 | 79 | 81 | 6 | 7 | 5 |
| M30 | 33 | 33.8 | 88 | 90 | 8 | 9.2 | 6.8 |
| (M33) | 36 | 36.8 | 97 | 99 | 8 | 9.2 | 6.8 |
| M36 | 39 | 39.8 | 106 | 108 | 10 | 11.2 | 8.8 |
| (M39) | 42 | 42.8 | 115 | 117 | 10 | 11.2 | 8.8 |