Abstract: An explosive perforating tool has an elongated barrel having a piston disposed substantially within. A radial passage extends from the outer surface of the barrel into the longitudinal cavity, thereby allowing the piston to be explosively driven from the tool through the radial passage. The piston has a longitudinal opening therethrough. When an explosive charge is set off increasing the pressure of a lubricating fluid within the longitudinal cavity, pressure is uniformly built up all around the piston and is the primary mode of force propelling the piston against the tubing. Vent openings are provided in the elongated chamber to allow the lubricating fluid to escape, thereby regulating the rate of pressure dissipation within the cavity to control the force with which the piston is propelled against the tubing. Spacers of varying size can be attached to the barrel to allow the tool to be used in different sizes of tubing.

Abstract: A roller arm centralizer to center a drill string in a well pipe. The arms of the roller arm centralizer include shoulders to limit movement of the arms in the direction of the centralizer body which prevents the arms from being locked in a straight line adjacent to the centralizer body. The shoulders also prevent the arms from being forced into an undesired configuration; wherein one arm is parallel to the body and the other two arms form a "V", by an abrupt decrease in the bore diameter. The roller arm centralizer remains operative when passing through relatively narrow sections of well pipe or through well pipe having abrupt changes in diameter.

Abstract: A calipering tool for use in a pipe and having a body and feeler means mounted with the body for engaging the surfaces of the pipe being calipered and with feelers moving in response to variations in the surface of the pipe, the improvement residing in mechanisms with the body for permitting the body of the calipering tool to be pumped in response to fluid pressure thereon into and out of the pipe for operation of the calipering tool.

Abstract: A calipering tool for use in a pipe and having a body and feeler means mounted with the body for engaging the surfaces of the pipe being calipered and with feelers moving in response to variations in the surface of the pipe, improvements residing in pairs of stylus members, including active and base-line styli, each active stylus adapted to engage a chart and move relative thereto in response to movements of a feeler and with each base-line stylus adapted to engage the chart adjacent the active stylus for providing an individual base-line for the respective active stylus for providing accurate dimensional recording and continuing thermal calibration of the calipering tool in response to temperature variations encountered within the pipe and a new removable stylus assembly capable of being removed from the calipering tool as a unit for repair and/or replacement as is necessary without requiring replacement of the entire calipering tool.