Position the straight edge of the weight on the o-ring's cross-section and raise the weight all the way to the top of the tube (as far as it will go). Release the weight and let it drop onto the o-ring. The weight will bounce. The height of the first bounce will rise to one of the four calibrated ranges.

This is crucial information for industries where exposure to extreme temperatures or harsh chemicals is common. For example, blue o-rings might signify resistance to low temperatures, while brown ones may indicate resistance to high temperatures.

Nitrile 'O' rings – best 'O' ring material for general-purpose reliability.