Lead of mechanical pencils
History of Spare Leads
Since the release of the Eversharp in 1838, the Spare Leads was made of graphite clay (same as pencil core), with a core diameter of 1.0 and 1.5 mm length of about 30mm. However, in 1962, a 0.5 mm synthetic resin core was released, and the core technological innovations took place.
The Tombow was produced in the graphite clay core ” MONO -Do”, and was approved by the Spare Leads JIS Display permission factory in 1961. Then, in 1965, the synthetic resin core “PLA” was released.