A distinct compartment at the tip of a stereocilium, distal to the site of attachment to the apical cell surface. It consists of a dense matrix bridging the barbed ends of the stereocilium actin filaments with the overlying plasma membrane, is dynamic compared to the shaft, and is required for stereocilium elongation. [ http://www.ncbi.nlm.nih.gov/pubmed/27565685 http://www.ncbi.nlm.nih.gov/pubmed/17021180 ]