This time he patented his new monofilament esthesiometer, and three patents issued. And the Weinstein Enhanced Sensory Test claims to have each of its SofTip monofilaments calibrated for applied force. The common monofilament is a single strand of nylon, which has the property of producing a characteristic downward force when buckled on a surface. Surprisingly, the downward force does not depend on the degree of bend of the monofilament. The actual force of downward contact increases linearly until the monofilament buckles, and then the actual force varies around the characteristic force for that monofilament.
Equations predict the characteristic force from the diameter and the length of the monofilament.
Heat and humidity also affect the characteristic force. But the actual force achieved depends on the integrity of the monofilament. Nicks, dents, scratches, dirt, cracks, etc. Each unbent monofilament is a right cylindrical solid. The buckling twists the monofilament, sending a three-dimensional crescent edge into the skin by varying degrees.