부산대학교 도서관

A tool for preparing broken stud bolts or the like for extraction by screw extractors has a guide for centering a center punch and/or a drill on a broken face of a stud. The guide is a nut and a shaft assembly. The nut has a central bore therethrough having a first portion threaded to mate with the stud threads and a second portion bored to just slide over the stud threads. The shaft assembly has a cylindrical shaft having a first end and a second end and an axial bore therethrough. The shaft includes a first externally threaded portion extending from the shaft first end of threads similar to those of the broken stud and an expandable sleeve attached to the shaft second end such that threading movement of the nut toward the shaft second end axially compresses the sleeve whereby the sleeve expands radially outward. The second end of the shaft has a conical end face. The shaft assembly and nut can be used in a variety of configurations that center the axial bore of the shaft over the stud's broken end face so that a drill or center punch can be inserted in the shaft's axial bore.