DIN 603 Coach Bolts (Cup Head Square Neck)
We supply DIN 603 coach bolts in steel grades 4.6 and 8.8, galvanised finishes and A2/A4 stainless steel, from M5 to M16. The domed head has no drive: the square neck below it pulls into timber or a square punched hole and holds the bolt still while the nut is tightened from the other side.
Also known as: coach bolt, cup square, carriage bolt, cup head square neck bolt, mushroom head bolt.
DIN 603 dimensions
| Diameter | Pitch | Head diameter | Head depth | Width of square | Depth of square |
|---|---|---|---|---|---|
| M5 | 0.8mm | 13.55mm | 3.3mm | 5.48mm | 4.1mm |
| M6 | 1.0mm | 16.55mm | 3.88mm | 6.48mm | 4.6mm |
| M8 | 1.25mm | 20.65mm | 4.88mm | 8.58mm | 5.6mm |
| M10 | 1.5mm | 24.65mm | 5.38mm | 10.58mm | 6.6mm |
| M12 | 1.75mm | 30.65mm | 6.95mm | 12.7mm | 8.75mm |
| M16 | 2.0mm | 38.8mm | 8.95mm | 16.7mm | 12.9mm |
When should I use a coach bolt instead of a hex bolt?
Use a coach bolt where the head side is inaccessible or needs a smooth, snag-free finish - timber structures, gates, playground and trailer work. The square neck stops the bolt turning, so the joint is made up entirely from the nut side. Where you can spanner both ends, a hex bolt such as DIN 931 gives more options.
Is DIN 603 the same as a carriage bolt?
Carriage bolt is the North American term for the same general cup-head, square-neck pattern known in the UK as a coach bolt. DIN 603 is the metric standard normally specified for this style; inch-series carriage bolts are dimensioned differently and should not be treated as interchangeable with metric DIN 603 product.
What materials are DIN 603 coach bolts available in?
DIN 603 coach bolts are available in A2 and A4 stainless steel across a wide range of metric sizes, and in steel grades 4.6 and 8.8 including galvanised finishes for external work. Tell us the size, length and finish and we'll price the options.
Need DIN 603 in a non-standard size or material?
Send us your drawing — specials quoted within 24 hours.