Fixing unit with an end imprint in a threaded terminal portion

摘要

A fixing unit includes a threaded terminal portion, with the end face having a hollow imprint with a multilobate shape. The distance between the peripheral edge of the imprint and the external peripheral surface of the portion varies between maximum (d1) and minimum (d2) values, the ratio of which is between about 1.25 and about 1.75, and preferably substantially equal to 1.5.