The primary vertical (or near-vertical) Stroke of a letterform, serving as the structural backbone of characters such as l, d, b, h, and the uprights of H, M, and N. Stem Weight is the main determinant of a Typeface apparent boldness and, together with the thinnest strokes, defines the stroke contrast ratio that distinguishes subgroups like Old Style Serif, Transitional Serif, and Modern Serif serifs.