The relevance of the work is caused by the need to increase the effectiveness of lubricating materials used in drilling technology. In general, their application leads to reduction in abrasive and fatigue wear of tool material, and increases the service life of drilling equipment, which is especially important for trouble-free operation and improvement of technical and economic parameters during well drilling. The aim of the research is to develop a procedure for selecting the optimal lubricant composition to improve the durability and tightness of drilling tool threaded connections by determining the thickness of the boundary layers of various lubricants at the specially designed unit. Research methods. Laboratory tests of properties (average thickness of lubricant layer, critical load, welding load, load wear index, wear indications) of various lubricating compositions were carried out at the developed test unit and using the four-ball friction machine ChMT-1. Results. The developed express method of lubricant selection according to load-carrying capacity based on the lubricating layer specific thickness calculation (the «pile» method) allows us to choose the optimum type from the lubricant compositions tested. The authors have determined the optimum percentage of additive content based on sulfur compounds added to improve the P-416 thread lubricant for pipe locking threads. The test unit developed is recommended for further preliminary studies of lubricant properties. Conclusions and recommendations. The authors have developed the express technique for optimal selection of lubricant according to its carrying capacity (technique of determining lubricant boundary thickness by the «pile» method), tested the MFA based on sulfur compounds. The research results showed that MFA additive in certain limits of the ratio to the lubricant increases the threaded connection susceptibility to loads, decreases rubbing surface wear and extends the service life of frictional elements. The authors recommend to apply the device developed for further studies of lubricant features.