Abstract: The object of the invention is to provide a novel pressure-tight screwed instrumentation fitting for a pressure vessel, which screwed instrumentation fitting has, for acceptable material costs, both a low assembly cost and a small space requirement and in which the measuring lines are not damaged.According to the invention this is achieved by two axial stops (24, 25) being formed in the cap nut (13) and by a third axial stop (26) being formed in the screw-in socket (10). The cap nut (13) and the screw-in socket (10) form a common interior space (15) which is bounded axially by the second and third stops (25, 26) and in which a multi-piece sealing insert (16) is arranged. The latter consists of a pressure-bearing front part (17), an end plate (18), a sealing sleeve (19) in between with a sealing element (20) arranged therein, and also the clamping ring (21). Both the sealing sleeve (19) and the sealing element (20) are produced from a sufficiently heat-resistant, deformable material, preferably steatite.