Closed, pre-slit form. ≥ M3 with tapered lead chamfer on both sides for easy start to the threading action and clean swarf evacuation in the direction of cutting. 1¾ turns lead chamfer. Tolerance zone 6e = with undersize approx. 0.03 − 0.04 mm. For tolerance class “medium”, when studs are provided with a galvanic protection coating.