DIN 603:2017 Large Round Head Square Neck Bolt has a large round bearing head and a square neck that prevents rotation. It is suitable for exposed joints where a smooth appearance and self-locating installation are desired.
Typical applications include wood structures, fences, shelving, vehicle accessories, agricultural machinery, and light steel-wood assemblies. The large round head provides better coverage, while the square neck seats into the prepared hole to resist turning.
During installation, the square neck should be matched with a square hole or suitable base material for reliable seating. For outdoor and wood-structure uses, corrosion protection, head appearance, and matching thread hardware strongly affect service life.

Dimensions unit: mm
| Thread size d | M5 | M6 | M8 | M10 | M12 | M16 | M20 | |
| P | Pitch | 0.8 | 1 | 1.25 | 1.5 | 1.75 | 2 | 2.5 |
| b | L≤125 | 16 | 18 | 22 | 26 | 30 | 38 | 46 |
| 125<L≤200 | 22 | 24 | 28 | 32 | 36 | 44 | 52 | |
| L>200 | / | / | 41 | 45 | 49 | 57 | 65 | |
| dk | Max. | 13.55 | 16.55 | 20.65 | 24.65 | 30.65 | 38.8 | 46.8 |
| Min. | 12.45 | 15.45 | 19.35 | 23.35 | 29.35 | 37.2 | 45.2 | |
| ds | Max. | 5 | 6 | 8 | 10 | 12 | 16 | 20 |
| Min. | 4.52 | 5.52 | 7.42 | 9.42 | 11.3 | 15.3 | 19.16 | |
| k1 | Max. | 4.1 | 4.6 | 5.6 | 6.6 | 8.75 | 12.9 | 15.9 |
| Min. | 2.9 | 3.4 | 4.4 | 5.4 | 7.25 | 11.1 | 14.1 | |
| k | Max. | 3.3 | 3.88 | 4.88 | 5.38 | 6.95 | 8.95 | 11.05 |
| Min. | 2.7 | 3.12 | 4.12 | 4.62 | 6.05 | 8.05 | 9.95 | |
| r1 | ≈ | 10.7 | 12.6 | 16 | 19.2 | 24.1 | 29.3 | 33.9 |
| r2 | Max. | 0.5 | 0.5 | 0.5 | 0.5 | 1 | 1 | 1 |
| r3 | Max. | 0.75 | 0.9 | 1.2 | 1.5 | 1.8 | 2.4 | 3 |
| s | Max. | 5.48 | 6.48 | 8.58 | 10.58 | 12.7 | 16.7 | 20.84 |
| Min. | 4.52 | 5.52 | 7.42 | 9.42 | 11.3 | 15.3 | 19.16 | |
| Thousand pieces of steel weigh ≈kg | - | - | - | - | - | - | - | |
| Thread length b | - | - | - | - | - | - | - | |
① Material:
a) Steel, strength grade: 4.6, 4.8, 8.8 according to DIN EN ISO 898-1
b) Stainless steel, strength grade: A2-70, A4-70 according to DIN EN ISO 3506-1
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Better Fastener is a professional fastener enterprise specializing in the manufacturing of steel washers, stainless steel washers, spring washers and sealingwashers. Founded in 2001 as a washer factory, the company expanded into a comprehensive enterprise integrating washers, nuts, bolts, spring nuts and other fastener products in 2010.
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