substantially the same diameter as that of the optical fiber 1 and has at its ends a recess 27 and a recess 28 of conical shape bushing 22 having elastic fingers 23 is applied on the cylindrical body 6 and by means of sleeve 19 and its chamfer 20 is positioned with its projections 24 in the central or second recess 13 so that the end sufaces abut the third shoulder 15 at the same time the terminal portion of the optical fiber 1 is inserted in the central bore of the ferrule 26 aided in this operation by the inner conical recess 27 so that its free end extends from said bore as shown in fig2 a conventional cutter for optical fibers not shown in the drawings having at its end a hollow semi sphere 29 provided with a central hole is arranged in the conical recess 28 of the ferrule 26 in such a way that the terminal portion of the optical fiber 1 is in the central hole of the hollow semi sphere 29 and the two surfaces the spherical surface of the semi sphere 29 and the conical surface 28 are in mutual contact the cutter is adjusted so as to cut the optical fiber 1 at a distance from the focus of the hollow semi sphere 29 which is exactly equal to the distance existing between the second shoulder 10 and the third shoulder 15 after cutting of the optical fiber 1 the cutter and the hollow semi.