7H

7H is an alphanumeric designation that appears in multiple domains, most commonly as a scientific isotope notation and as a material or product grade.

As an isotope designation, 7H (or hydrogen-7) denotes an isotope of hydrogen with one proton and six neutrons. It is one of the most neutron-rich hydrogen isotopes and is highly unstable; experiments have reported it only as an unbound resonance produced in high-energy nuclear reactions. Its existence and properties are of interest in nuclear physics for studies of nuclear forces in extreme neutron-to-proton ratios, but 7H has no practical applications outside research due to its very short lifetime.

In art and technical drawing, 7H refers to a pencil hardness grade on the HB/H scale. Grades labeled H become progressively harder and lighter in mark; 7H is an especially hard grade that leaves pale, fine lines suitable for precision drafting, archival drawings, or when minimal graphite residue is required. It is less common in general writing or shading because of its light mark and greater wear on drafting surfaces.

Beyond these uses, 7H appears as a model, batch, or code identifier in manufacturing, transportation, and electronics, where alphanumeric tags help distinguish variants, products, or routes. The meaning in such cases is context-dependent and defined by the issuing organization.