A carriage bolt is also called coach bolt or round head square neck bolt or mushroom bolt.
It is distinguished from other bolts by its head: the shank of the bolt is circular for most of its length, as usual, but the portion immediately beneath the head is formed into a square section. This makes the bolt self-locking when placed through a square hole, or a round hole in most wood. This allows the fastener to be installed with only a single tool, a spanner or wrench, working from one side. The head of a carriage bolt is usually a shallow dome. The squared section is of the same size as the diameter of the bolt shank, with a plain unthreaded shank.
Carriage bolts were developed for use through iron strengthening plates on either side of a wooden beam. It is commonplace though to use them into bare timber, the squared section giving enough grip to prevent rotation.
Carriage Bolt
DIN 603 Weight (KG/1000pcs)
| l\d | M5 | M6 | M8 | M10 | M12 | M16 | M20 |
| 16 | 4 | 6.9 | |||||
| 20 | 4.5 | 7.6 | 13.8 | 22.7 | |||
| 25 | 5.1 | 8.5 | 15.4 | 25.2 | |||
| 30 | 5.9 | 9.6 | 17 | 27.7 | 45.7 | ||
| 35 | 6.7 | 10.7 | 19 | 30.2 | 49.4 | ||
| 40 | 7.5 | 11.8 | 21 | 32.7 | 53.1 | ||
| 45 | 8.3 | 12.9 | 23 | 35.8 | 56.8 | ||
| 50 | 9.1 | 14 | 25 | 38.9 | 61.2 | 119 | |
| 55 | 9.9 | 15.1 | 26.9 | 42 | 65.6 | 126 | |
| 60 | 10.7 | 16.2 | 28.9 | 45.1 | 70 | 133 | |
| 65 | 11.5 | 17.3 | 30.9 | 48.2 | 74.4 | 141 | |
| 70 | 12.3 | 18.4 | 32.9 | 51.3 | 78.8 | 149 | 247 |
| 80 | 13.9 | 20.6 | 36.8 | 57.5 | 87 | 165 | 272 |
| 90 | 22.8 | 40.8 | 63.7 | 96 | 181 | 297 | |
| 100 | 25 | 44.8 | 69.9 | 105 | 197 | 322 | |
| 110 | 27.2 | 48.8 | 76.1 | 114 | 213 | 347 | |
| 120 | 29.4 | 52.8 | 82.3 | 123 | 229 | 372 | |
| 130 | 31.6 | 56.8 | 88.5 | 132 | 245 | 397 | |
| 140 | 32.8 | 60.8 | 95 | 141 | 261 | 422 | |
| 150 | 35 | 64.8 | 101 | 150 | 277 | 447 | |
| 160 | 107 | 159 | 293 | 497 | |||
| 180 | 119 | 177 | 325 | 547 | |||
| 200 | 131 | 195 | 357 | 597 |
