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Hydraulic power cylinders are the main bearing elements of powered supports at mining enterprises, ensuring reliable fixation of the roof in the required working position, as well as providing advancement of the support in the face. Thus, hydraulic power cylinders ensure stoping safety, so strict requirements are im-posed on them both in terms of workmanship and operational reliability. To ensure reliability and efficiency of powered support operation in faces, it is necessary to ensure stable service life of their hydraulic props, which mainly depends on the quality of manufacturing of mating surfaces and the accuracy of assembling functional joints. The required accuracy of hydraulic prop joints is achieved by selective assembly, which allows ensuring the specified technical requirements and service life of the joints. At the same time, along with the issues of ensuring the accuracy of assembling the props to provide proper safety of the face operation, it is extremely important to identify and analyze the causes of dimensional wear of critical parts of the joints, leading to decreasing service life of the hydraulic props in the course of exploitation. In the paper, using the methods of the analytical theory of bases, the reasons for formation of positional variations of the parts of the powered support hydraulic prop joints in the course of assembling and operation of the unit are identified and described. It was found that arising mismatches and formation of local stress zones on the cylinders, pistons and rods, characterized by intense wear, occurs due to the uncertainty of basing (positioning) of rod and piston in hydraulic cylinder. The dependencies allowing calculating deviation of the rod axis from the required position, taking into account the initial clearance gap in the joints and the adopted design parameters of the hydraulic cylinder, have been obtained.