Patent ID: 7980794

Claim:
A ring with a cutting edge detachably fixed to a drilling tool and having a cutting edge insert which machines a peripheral edge of a hole bored by the drilling tool, comprising: a ring portion having: an insertion hole allowing the drilling tool to be inserted in the direction of an axis thereof; and a circular shape in plane view, wherein the ring portion has a portion on the inner peripheral surface provided with a recess formed radially outward, a circular-arc arm portion, which extends in the peripheral direction from one peripheral end of the inner peripheral surface toward the other peripheral end thereof, in the opening edge of the recess facing the inner peripheral surface and is elastically deformable in the radial direction, is formed integrally in the ring portion, and wherein the circular-arc arm portion is pressed axially inward by a fastening screw threadedly attached to a threaded attachment hole which goes through the ring portion in the radial direction and is opened to a bottom surface of the recess.