This page lists bolt grade 8.8 with tensile strength 800 MPa, yield strength 640 MPa, hardness 22–32 HRC. Tensile strength is the stress at which the fastener fails in tension; yield strength is the stress at which it starts to deform permanently; hardness describes resistance to indentation.
Compare these figures with the loads in your own design calculation rather than with other grades in isolation. Where a value is not defined for the class, this library shows a dash rather than an estimate.
In this library the class is listed against DIN933, ISO4017, DIN931, ISO4014, DIN912 and ISO4762. Property classes are defined per product standard, so confirm the class marking and the standard's own table before releasing a batch or accepting a certificate.
The design verification rules below are a checklist for a specific joint: 6 rules covering the checks that matter most for this class.
The factor of safety and the acceptable preload still have to come from your project's engineering requirements. Related pages: mechanical properties hub, fastener materials and surface treatment.