Safe working load (SWL) is the load that a lifting device such as a crane, a cherry picker, or a lifting arrangement can safely lift, suspend or lower. Other synonyms include working load limit (WLL), which is the maximum working load designed by the manufacturer. The load represents a mass or force that is much less than that required to make the lifting equipment fail or yield. The SWL is calculated using a given safety factor (SF) which for lifting slings could be given for example 5:1. The failing load is also known as minimum breaking load (MBL).
Factor of safety (FoS), also known as safety factor (SF), is a term describing the structural capacity of a system beyond the expected loads or actual loads. Essentially, how much stronger the system is than it usually needs to be for an intended load. Safety factors are often calculated using detailed analysis because comprehensive testing is impractical on many projects, such as bridges and buildings, but the structure's ability to carry load must be determined to a reasonable accuracy.
Many systems are purposefully built much stronger than needed for normal usage to allow for emergency situations, unexpected loads, misuse, or degradation.
Ultimate load, strength requirements are specified in terms of limit loads (the maximum loads to be expected in service) and ultimate loads (limit loads multiplied by prescribed factors of safety). With respect to aircraft structure and design, ultimate load is the amount of load applied to a component beyond which the component will fail.
A chain is a series of connected links which are typically made of metal. A chain may consist of two or more links.
Chains are usually made in one of two styles, according to their intended use:
Those designed for lifting, such as when used with a hoist; for pulling; or for securing, such as with a bicycle lock, have links that are torus shaped, which makes the chain flexible in two dimensions (The fixed third dimension being a chain's length.)
Those designed for transferring power in machines have links designed to mesh with the teeth of the sprockets of the machine, and are flexible in only one dimension. They are known as Roller chains, though there are also non-roller chains such as block chain.
Wire rope is a type of rope which consists of several strands of metal wire laid (or 'twisted') into a helix. Initially wrought iron wires were used, but today steel is the main material used for wire ropes.
Historically wire rope evolved from steel chains which had a record of mechanical failure. While flaws in chain links or solid steel bars can lead to catastrophic failure, flaws in the wires making up a steel cable are less critical as the other wires easily take up the load. Friction between the individual wires and strands, as a consequence of their twist, further compensates for any flaws.