smaller than those of the associated back off surfaces 9 and 11 the included angle u03b1 at the cutting edge of the high tooth 4 is smaller than the included angle u03b2 of the cutting edge of the low tooth 5 in the illustrated embodiment the angle u03b1 is 120 u00b0 and the angle u03b2 is 150 u00b0 the difference in height between the cutting points p4 and p5 is very small say 0 3 mm in the drawings 12 represents lands defined on the outer side of the annular wall between the spiral grooves and 13 represents gullets formed between the successive cutting teeth the shank portion 3 is secured to the arbor of an electrically powered drill not shown as the drill is lowered with the annular hole cutter rotating an annular groove is formed in a workpiece as will be described below first the high teeth 4 cut a groove shallow in the workpiece with the central cutting edge portions x of the teeth width followed by the trailing low teeth 5 cutting the opposite side portions of the groove cut shallow by the central portions x of the leading high teeth 4 with the opposite lateral cutting edge portions y of the low teeth 5 whereby the full width of the groove is cut in three divisions the low teeth 5 do not engage with and do not perform the cutting operation on that central portion of the groove which has been cut by the high teeth 4 the cutting operations.