Cone penetration (worked penetration) is a numerical value that expresses the hardness of grease (paste). The test grease is inserted into a container and a plunger is stroked 60 times while the test apparatus and grease are maintained at a temperature of 25 °C. Immediately thereafter, a specially-configured cone is placed just above the grease so that the cone penetrates the grease by its own weight, and after a specific time interval, the penetration depth is measured in mm and multiplied by 10. The larger the worked penetration, the softer the grease (paste). NLGI grades determined by worked penetration ranges are listed in the table as the following. The higher the NLGI grade, the harder the grease.

【NLGI Grades and Worked Penetration Ranges】