0.5 mm. Technology strength, Stein structure. Frame supports from the inner core. Hard to break, so! Stein established the silica enhanced frame inside the core. Supports the entire core from the inside this frame structure for the highest level of intensity achieved. This is a brand new sharp replacement Wick, incorporating the technology strength, in addition to smooth. The case lid by turning the wick. -Pencil holder ?? core diameter: 0. 5 mm-core colors BL (blue wire)-core length: 60 mm-core units: 20-quantity: 1 piece