A filter device positionable within a blood vessel for trapping blood clots in that vessel, the filter device comprising a head with a plurality of divergent legs each secured at its proximal end, to the head, each leg having a hook arranged at its distal end.Each leg has a radially outwardly directed radius of curvature to create a conical configuration to the filter assembly, while distributing the stress concentration along the length of the bend, so that the elastic limit of the material, stainless steel in this embodiment, is not exceeded, and which permits compact delivery of the filter, and adequate radially directed force to permit slight hook penetration of a vessel wall.