A keeper for an implant comprising (a) a keeper body made of a soft-magnetic material, which comprises a recess for receiving a head of an abutment having a female thread, and a female thread extending along a center axis to have communication with the recess and having a larger nominal diameter than that of the female thread of the abutment; and (b) a stepped screw member comprising a small-diameter screw portion threadably engageable with the female thread of the abutment, and a large-diameter screw portion threadably engageable with the female thread of the keeper body; the keeper body being strongly fixed to the abutment by the stepped screw member, when the keeper body is rotated in a threadably engaging direction, after the female thread of the abutment threadably engages the small-diameter screw portion, and after the female thread of the keeper body threadably engages the large-diameter screw portion.