A tool and process for flaring an open end of a hollow metal tube utilizes a body having an elongated working surface which is substantially conical in shape so that one end of the working surface is a smaller end and so that the other end of the working surface is a larger end. The working surface further includes at least two outwardly-extending, smooth-surfaced protuberances which are regularly spaced around the working surface and which extend along the length thereof so that by rotating the tool about its longitudinal axis, inserting the smaller end of the working surface into an open end of a hollow metal tubing, and then urging the working surface against the open end of the metal tubing, the open end of the metal tubing is flared by the working surface.