Abstract: This disclosure relates to a drill for forming an undercut cavity in a hole in concrete, for an anchor bolt. The drill has forward and rearward ends, and comprises a body having an axially extending bore forming a generally cylindrical wall, the bore being open adjacent said forward end. A wedge center is slidably mounted within the bore, and connecting means is fixed to said center and axially slidably engages the body so that the body and the center rotate together. The center is spring-urged toward the forward end relative to the body. The body has a blade adjacent its forward end and a cutting tooth is fixed to the blade. The center has guide jaws adjacent said forward end and the jaws extend radially outwardly toward the forward end, whereby as the body moves toward the forward end relative to the center, the blade slides on the jaws and the tooth moves radially to form the cavity.