ISO 9177-2:1989 Preview
Mechanical pencils -- Part 2: Black leads -- Classification and dimensions
This standard was last reviewed and confirmed in 2015. Therefore this version remains current.
Two types are available, black leads in which the binding agent is an organic polymer (designated by the letter "P"), and black leads in which the binding agent is clay (designated by the letter "C"). Classification is made according to the degree of hardness. Part 1 deals with the classification, dimensions, performance requirements and testing.