Hard facts
Theory of hardness testing
Back to overviewA Knoop hardness value consists of the following components:
1. The numeric hardness value;
2. The two letters "HK", standing for "Hardness according to Knoop";
3. The applied test load in kgf;
4. According to ISO 4545: The dwell time of the test load, but only if this is not between 10 and 15 seconds (uncommon in practice)