DIN 603 carriage bolts are a type of fastener that are commonly used in construction and woodworking projects. These bolts have a square neck under the head, which helps to prevent the bolt from turning when it is tightened. The square neck also allows for easy installation with a wrench or pliers. Carriage bolts are typically made from steel and have a smooth, rounded head that is designed to be flush with the surface of the material being fastened. They are often used to secure metal or wooden components together, providing a strong and reliable connection.