Calculate stress area, proof stress, and proof load for metric bolts in classes 8.8, 10.9, and 12.9.
Set the inputs and start the calculation.
Calculate a standard-related proof force from tensile area and property class.
Thread size or Aₛ, property class and selected fraction of proof or yield stress define the force.
Aₛ converts a material proof stress into force for the actual thread. Property class is essential: the same size can have a very different proof force in another class.
Proof force equals tensile area times allowable proof stress. It supports classification and is not an automatic assembly setting.
Aₛ = 58 mm² at 600 MPa proof stress gives 34.8 kN.
Sources and limits: ISO 898-1 specifies mechanical properties and proof stresses for metric bolts.
Calculate a standard-related proof force from tensile area and property class.
Bolt calculations describe a joint through geometry, preload, friction and material limits. Preload clamps the parts; external load, embedding and temperature change the reserve.
Proof force equals tensile area times allowable proof stress. It supports classification and is not an automatic assembly setting.
Thread size or Aₛ, property class and selected fraction of proof or yield stress define the force. Aₛ converts a material proof stress into force for the actual thread. Property class is essential: the same size can have a very different proof force in another class.
Select thread size or enter the tensile stress area Aₛ directly, choose the property class and the desired fraction of proof stress. The calculator returns the resulting proof force.
Aₛ = 58 mm² at 600 MPa proof stress gives 34.8 kN.
Aₛ converts a material proof stress into force for the actual thread. Property class is essential: the same size can have a very different proof force in another class. A passing result means only that the selected model stays within the entered limits. Tightening scatter and real contact surfaces may govern residual clamp force.
Area in mm², stress in MPa, result in kN.
Assessing how much reserve a chosen assembly preload has relative to the normative proof force, or reviewing test reports referencing ISO 898-1.
ISO 898-1 specifies mechanical properties and proof stresses for metric bolts.
Common mistake: Don't use the proof force as an allowable operating or assembly preload – it is a normative test value close to yield strength and above what's sensible for continuous-duty preload. Don't confuse proof stress with tensile strength; both differ by property class.
Proof stress is normatively set slightly below the property class's guaranteed minimum yield strength; proof force is the force at which the bolt must just barely show no relevant permanent deformation.
Common values are 70 to 90% of proof stress, depending on tightening method and its scatter; the applicable standard or design guideline governs.
No, it depends directly on the property class – an 8.8 bolt has a noticeably lower proof force than a 12.9 bolt of the same size.
Thread size and property class determine stress area, proof stress, and proof load.
Proof load combines stress area and proof stress for a property class. Joint design additionally requires the nut, engagement, assembly process, and service loading.
Proof load is not a universal safe limit for the assembled joint.
A high-strength bolt cannot compensate for an unsuitable nut or weak tapped material.
Assess elevated or low temperature, corrosion, and hydrogen effects separately.
Property classes and proof loads for nuts with specified classes.
Product geometry and dimensions for the selected bolt type.
Turn the component characteristic into a defensible joint assessment.