A thread former for manufacturing an internal thread in a metal workpiece, the thread former comprising:
- a shaft having a first end and a second end;
- a mounting section connected to the first end of the shaft for mounting the thread former to a spindle of a machine tool;
- and
- a forming section connected to the second end of the shaft, wherein the shaft, the mounting section and the forming section have a common central axis of rotation, the axis of rotation extending in a longitudinal direction, wherein the forming section includes a plurality of lubrication grooves extending parallel to the axis of rotation, wherein the forming section also includes a plurality of ridge sections extending along a circumference of the forming section, wherein the plurality of ridge sections are arranged for forming the internal thread in the metal workpiece, and wherein, in a circumferential direction, each two of the plurality of ridge sections are separated by one of the plurality of lubrication grooves, at least the one of the plurality of lubrication grooves, when projected into a projection plane perpendicular to the axis of rotation, is asymmetrical with respect to any radius intersecting a surface of the lubrication groove, wherein, when projected into the projection plane, the first part-surface has a first top angle, which first top angle is formed between a first radius intersecting the trailing end point of the first ridge section and a second radius intersecting a first midpoint on the first part-surface, the second part-surface has a second top angle, which second top angle is formed between a third radius intersecting the leading end point of the second ridge section and a fourth radius intersecting a second midpoint on the second part-surface, the first midpoint and the second midpoint each having a radial distance from the axis of rotation equal to half the sum of the maximum radial extension of the first ridge section and the radial distance of the minimum point from the axis of rotation, and wherein the first top angle is larger than the second top angle, and wherein, when projected into the projection plane, the first part-surface has a first top angle, which first top angle is formed between a first radius intersecting the trailing end point of the first ridge section and a second radius intersecting a first midpoint on the first part-surface, the second part-surface has a second top angle, which second top angle is formed between a third radius intersecting the leading end point of the second ridge section and a fourth radius intersecting a second midpoint on the second part-surface, the first midpoint and the second midpoint each having a radial distance from the axis of rotation equal to half the sum of the maximum radial extension of the first ridge section and the radial distance of the minimum point from the axis of rotation, and wherein the first top angle is larger than the second top angle.