An eye bolt is a bolt with a loop at one end. It is a mechanical fastener with a threaded shaft and a head forming a ring. They are used to firmly attach a securing eye to a structure, so that ropes or cables may then be tied to it. A common use is to create a lifting eye so that a crane can be attached to machinery, with special-purpose lifting eyes rated for their safe working load. High-strength eyebolts have forged heads that normally include a substantial shoulder. The shoulder enables them to support significant off-axis loads. The ability to support off-axis loads is often important in lifting applications where lifting slings with multiple legs are used to attach to multiple lifting eyes. When lifting machinery, it is common for an eyebolt to be screwed directly into a tapped hole in the structure. In this case, an eyebolt is required that is fully threaded all the way up to the shoulder. When an eyebolt is intended to be inserted through a hole and fastened by a nut on the other side, it is better if there is a shank. A shank is an unthreaded section of the shaft, below the shoulder, which provides a better transfer of load into the surface of the hole and is less likely to crack under a fatigue loading.