Adhesive & Undercut AnchoringUndercut anchors are not your typical anchors. The bottom of the hole has a notched opening, or undercut, made either with a special drill bit or with an anchor that has a drilling device at the end of the bolt. When in place, the anchor uses the compressive strength of the concrete to resist the load, unlike a wedge anchor, which relies on the concrete's tensile strength.
There are two types of undercut anchors. The standard type requires drilling the hole, followed by drilling the undercut with the special bit. The second type is called a self-drilling anchor, which doesn't require the additional bit.