see working-load limit.
Safe Working Load (SWL) sometimes stated as the Normal Working Load (NWL) is the maximum safe force that a piece of lifting equipment, lifting device or accessory can exert to lift, suspend, or lower, a given mass without fear of breaking. Usually marked on the equipment by the manufacturer. It is a calculation of the Minimum Breaking Strength (MBS) aka Minimum Breaking Load (MBL) divided by its risk factor, usually ten to one (10:1 or 1/10) for lifting equipment although depending on the application, other fractions may be used such as 1/4, 1/5 and 1/6.
Other synonyms include Working Load Limit (WLL), which is the maximum working load designed by the manufacturer. This load represents a force that is much less than that required to make the lifting equipment fail or yield, also known as the SWL the WLL is calculated by dividing MBL by a safety factor (SF). An example of this would be a chain that has a MBL of 2000 lbf (8.89 kN) would have a SWL or WLL of 400 lbf (1.78 kN) if a safety factor of 5 (5:1, 5 to 1, or 1/5) is used.
WLL = MBL / SF