Undercut anchors are anchors with parts that spread and mechanically interlock with the concrete base material. Much lower expansion forces are produced during installation and loading than with expansion anchors. Undercut anchors allow for close edge distances and small anchor spacing. If the shape of the undercut is well adapted and its depth is sufficient, an undercut anchor functions virtually identically to cast-in fixings, i.e. both achieve the same ultimate loads, because the undercut anchor optimally uses the high resistance to compression forces of the concrete. Undercut anchors are used to fix medium and high loads with an excellent reliability.