a tamper resistant valve actuator for a fire hydrant has a bullet shaped nose presenting a nongrippable conical surface . three equally spaced shallow recesses are provided in the conical surface at a common elevation . a special wrench includes radially projecting set screws adapted for complementary fit within the recesses and adjustable tightening thereto for operating the valve stem . the actuator is designed for installation on conventional hydrant assemblies and in substitution of the existing pentagon head operating nut . in a modified embodiment , the valve operating nut is provided with a valve stem socket for compatibility with another form of hydrant assembly . in addition , the wrench receiving recesses are placed in a variant pattern .