2H

2H is a designation used in several technical fields, most commonly to refer to a pencil hardness grade and to a hexagonal crystal polytype in materials science.

In pencils, 2H denotes a lead of higher hardness. The H stands for hard, and higher numbers indicate even harder leads. A 2H pencil yields a light, precise line and is favored for technical drawing, drafting, and fine lettering. The increased hardness comes from a higher proportion of clay binder relative to graphite, making the lead less prone to smudging and capable of maintaining a sharp point, though it can be more prone to breakage if pressed too hard against a surface.

In crystallography and materials science, 2H designates a hexagonal polytype with a two-layer repeating stacking sequence. This notation is used for several compounds, including 2H-SiC (silicon carbide) and 2H transition metal dichalcogenides such as 2H-MoS2 and 2H-WS2. The 2H label distinguishes it from other polytypes of the same chemical composition, such as 4H or 6H, which differ in stacking order and resulting physical properties. The properties of a 2H material depend on the specific chemical system and on external conditions like temperature, pressure, and doping.

The meaning of 2H thus depends on context, typically referring to either a pencil grade or a hexagonal crystal polytype in science and engineering.