Abstract: A pipe cutter having guidance means for cutting a pipe on a plane generally perpendicular to the longitudinal axis of the pipe. A power tool imparts a rotational torque to a shaft having a circular cutting blade carried thereon at substantially right angles thereto. The guidance means, having a pipe contacting surface, is journalled onto the end of the shaft, so that rotation of the shaft and blade will not cause rotation of the guidance means. The method involves aligning the rotating blade at a preselected cutting point, imbedding the blade into the walls of the pipe until an arcuate portion of said walls is cut, and thereafter imparting an orbital motion to the shaft about the pipe axis to achieve the pipe cutting operation.

Abstract: Disclosed are plugs and fasteners which deter unauthorized removal through the use of rotationally symmetric engagement recesses. The invention also provides special tools with projections complementary to the plug and fastener recesses and thereby permit easy removal of the plugs and fasteners without damage. An exemplary embodiment of an inventive plug contains a two-stage recess in lieu of the standard hexagonal head; each of the recess stages is rotationally symmetric, and the two stages have non-coinciding symmetry axes. The rotational symmetry of the recess stages defeats any attempt to remove an inserted plug by forcing commonly available tools, such as hex or square drivers and blade or Phillips screwdrivers, into the recess. An inventive tool for use with this embodiment has a two-stage projection complementary to the recess.