Indentation hardness
Hardness measurements quantify the resistance of a material to plastic deformation. Indentation hardness tests compose the majority of processes used to determine material hardness, and can be divided into two classes: "microindentation" and "macroindentation" tests. Microindentation tests typically have forces less than . Hardness, however, cannot be considered to be a fundamental material property. Classical hardness testing usually creates a number which can be used to provide a relative idea of material properties. As such, hardness can only offer a comparative idea of the material's resistance to plastic deformation since different hardness techniques have different scales.
Knot thickness
The thickness is defined using the simpler concept of the local thickness τ("x"). The local thickness at a point "x" on the link is defined as
where "x", "y", and "z" are points on the link, all distinct, and "r"("x", "y", "z") is the radius of the circle that passes through all three points ("x", "y", "z"). From this definition we can deduce that the local thickness is at most equal to the local radius of curvature.