Disclosed is a holder which may be used for mounting equipment, such as sensing apparatus, within an otherwise closed environment, and an extractor tool for inserting and retrieving the holder and attached equipment. In an operating configuration the holder is double-sealed to a landing nipple mounted on the container against communication of high pressure fluid out of the container. With the extractor tool mounted and sealed on the landing nipple also, a placement member within the extractor tool may engage the top of the holder to extract the holder from sealing engagement with the landing nipple. Two independent gear boxes are provided whereby translational and rotational motions may be separately imparted to the placement member. The holder is anchored to the landing nipple by threaded engagement between the landing nipple and a drive screw section of the holder. A separate seal section of the holder is rotated during the insertion procedure until a preselected orientation of the seal section is achieved. With the orientation of the seal section fixed, further insertion of the holder into the landing nipple without rotation of the seal section effects a metal-to-metal seal, in addition to a packing-type seal, between the seal section and the landing nipple.