a fishing device not shown may be attached to the lower end of the drill string for engagement with drilling equipment to be retrieved similarly the jarring apparatus can comprise part of a drill string to dislodge the drilling components if the same becomes stuck in the well bore in order to dislodge such equipment or components when stuck in the well bore an upward jarring blow is delivered to the drill string by jarring apparatus generally referred to by reference numeral 12 carried by a mandrel generally denoted by reference numeral 14 the mandrel being slideably and telescopingly received within the drill string the drill string as shown in fig1 includes an outer cylindrical barrel member 16 to which an adaptor 18 is threadedly connected at the upper end the adapter having an annular anvil surface 20 the adapter is also provided with seals including the seal element 22 in wiping contact with the cylindrical surface of the mandrel body 24 spline slots 25 are formed in the cylindrical surface of the mandrel body 24 for receiving keys 26 which are retained in the confronting surface of body 18 as more clearly seen in fig2 through which torque is transferred between the body 24 and the adapter 18 threadedly connected to the mandrel body 24 is a body 28 of a fluid pressure holding device which projects radially outwardly and presents an annular hammer surface 30 that is axially spaced from the anvil surface 20 in the collapsed position of the mandrel and.