N, daN, kN & kgf

Kilonewtons (kN) or Kilograms (kg) are commonly used for stating safety holding values of fasteners, anchors and more in many industries. They are also often used in the specifications for rigging, lifting, suspension and anchor hardware and fittings (e.g. Wire Rope and Eye Nuts). The safe working loads in both tension and shear measurements can be stated in kN or (properly) kgf as “Tensile Strength = xxx.x kg” or “Minimum Breaking Strain (MBS) = xxx.xkN”.

1 kN equals 101.97162 kilograms of force (kgf), but multiplying the kN value by 100, you get a slightly pessimistic and easier to calculate value if you’re in a rush.

Technically, the newton (symbol: N) is the International System of Units (SI) derived unit of force. It is named after Isaac Newton in recognition of his work on classical mechanics, specifically Newton’s second law of motion. SI defines one newton (1 N) as the force required to accelerate a mass of one kilogram at a rate of one meter per second squared (one meter per second per second) in the direction of the applied force. The measurement of this force is commonly express in in kilonewtons (symbol: kN) or kilograms-force (symbol: kgf – often expressed as simply kg) or less commonly – dekanewtons (symbol: daN).

Gravity provides the means of converting a mass to a force measurement as (on Earth) a mass of 1 kg exerts a force of approximately 9.8 N (down), or 1.0 kilogram-force, 1 kgf. And since 9.8 (rounded up with zero decimals) is 10 – this leads to the approximation of 1 kg corresponding to 10 N and 1kN corresponding to 100 kgf (mentioned above) which is sometimes used as a rule of thumb in everyday life and in engineering. Technically, the conversion is actually:

1 kilogram-force (kgf) 9.80665 newtons (N)
1 kilonewton (kN) 100 dekanewton (daN) = 1000 newtons (N) and
1 dekanewton [daN) = 10 newtons (N)

An amazing rule of thumb to help remember a Newton (N) follows:

On earth, 1 N is approximately 100 grams (g) which is similar to the mass of an apple. Thus, you can think of 1 N as being hit on the head by Newton’s Inspiration.

Examples of how the strength of an item might be stated…

MBS 18kN = 1800 kgf approx 1800 daN
“Breaking strain 1800 daN”= 18 kN = approx 1800 kg
“Breaking strain 2000 daN”= 20 kN approx 2000 kg
“Breaking load 2500 kg”= approx 25 kN = 2500 daN
“Breaking strain 2500 daN”= 25 kN = approx 2500 kg
“Guaranteed load 26 kN” 2600 daN = approx 2600 kg
“Breaking load 32 kN”= 3200 daN approx 3200 kg
“Breaking strength 40 kN”= 4000 daN approx 4000 kg

For more info, see Newton (unit) – Wikipedia, the free encyclopaedia

MBS vs WLL vs SWL

MBS and MBL represent the level of force required to make the fitting, hardware, chain, or rope fail or yield (terminal deformation), which is usually known as the Minimum Breaking Load (MBL) or Minimum Breaking Strength (MBS). MBS is usually supplied

either on a Mill Certificate which is applied to a batch number which is marked on the equipment shipped by the manufacturer, or
derived by measurements taken of a Standardized fastener (e.g. DIN Oval Copper Swage Sleeve) attachment with reference to standardized tables (e.g. Talurit Oval Swaging Tables)

Working Load Limit (WLL) represents a force that is much less than that of the Minimum Breaking Load (MBL) or Minimum Breaking Strength (MBS). WLL is calculated by dividing the MBL by a Safety Factor (SF) i.e. WLL = MBL / SF. It ultimately represents the maximum working load designated by the manufacturer as the force that a piece of lifting equipment, lifting device or accessory can be expected to accommodate to lift, suspend or lower a mass without fear of breaking which may be applied in a repeatable manner. The WLL is usually supplied

as markings/stamps on the equipment by the manufacturer in compliance with a stated standard or
derived by applying an SF to a certified MBS of an item.

Safe Working Load (SWL) is a colloquial non-certifiable designation. It can be set by an Engineer on a project basis after a thorough examination and understanding of the pertinent risks and possible outcomes. Basically, and Engineer chooses his/her own ‘reasonable’ level of force that an item must survive in a given context. This choice of force leads to a SF for a particular project. The SF is then applied the MBS to arrive at a project specific choice of materials. The selection of an SF value on a project specific basis can best be understood by imagining and comparing the risks and acceptable outcomes of failure when planning and completing the following two projects:

hanging a struggling elephant in a cage overtop of a collection of premature infants, versus
hanging a rock in a bottomless and unpopulated mine shaft.