Commonly used names for Carriage bolts are: coach bolt or round head square neck bolt. The main characteristic of this bolt is its head and square portion under the head, which is designed same as the diameter of the shank and it prevents bolt from turning when dropped in the round or square hole, acting as a locking element.
Grade 2: SAE J429 GRADE 2 SQUARE NECK CARRIAGE BOLT. ASME B18.5 1990 IFI-7
Grade 2: Up to 6” in length are full thread, longer are partial threaded
Grade 5: Mostly partial thread