The application will determine proper load. The following factors are important for live loading a bolted joint:
Decide what load or torque should be used for a sound joint design. If the joint is a flange, the gasket manufacturer should provide this value. If the joint is a bus (electrical) connection, the designer of the system should provide this value.
Decide which material the Belleville spring should be. We generally suggest a material that is similar to the bolt material.
If the Belleville spring may be used at its flat load, use a spring whose flat load is close to the design preload. It may be necessary to use multiple Belleville springs in parallel in order to acheive the requisite flat load. Ideally, the design preload will be 90%-100% of the flat load.
Confirm the spring arrangement fits into the space contraints of the application.