Nominal Arm Length
Nominal arm length is the maker’s size designation, commonly in inches, such as 9-inch or 12-inch.
It is not a precise installation measurement. Effective length runs from the arm’s pivot—the point it turns around—to the stylus tip; mounting distance runs from that pivot to the platter spindle. Neither is necessarily an exact conversion of the nominal inch label.
Nominal Arm Length — Tonearm
Use nominal length to compare arm sizes at a glance. Before choosing an arm, check the exact length version’s mounting drawing, required mounting distance and physical clearances. Two arms with the same nominal size need not fit the same mounting position. Follow that model’s cartridge-alignment instructions.
Keep the maker’s stated size, including fractions such as 9.5 inches; do not round it or calculate it from another dimension. A larger nominal number alone does not establish better sound.