Each Rapidograph® pen features a stainless steel nib in one of 10 sizes from the hairline 6x0 (.13mm) nib to the large 4 (1.20 mm) nib. Replacement points are available for all pen sizes. Alternative tungsten carbide nibs are twice as strong as steel and are available in sizes 3x0, 00, 0. The pen also features a white plastic barrel with a refillable ink reservoir (pens do not come filled with ink), and a color-coded cap for nib selection.

The double-seal cap is air-tight to keep the nib from drying out. Each pen is identified by a standard nib size or by its line width expressed in millimeters. Note: "nib" and "point" are terms used interchangeably but point sizes do not correspond to points in the point/pica system of typographic measure.