Any measurable or observable characteristic related to the shape, structure, color, or pattern of the mechanosensitive hair bundles located at the apical end of cochlear OHCs; each hair bundle is normally composed of ~100 nonmotile, actin-filled microvilli (stereocilia) arranged in rows of increasing height and coupled to one another by morphologically distinct links: tip links, horizontal top connectors, shaft connectors, and ankle links; most hair bundles also possess a single motile kinocilium immediately adjacent to the tallest (outermost) row of stereocilia; a fifth link type, the kinocilial link, connects the kinocilium to its neighboring stereocilia.