This technical brief clarifies origins of the piston ring conformability bounds presented by Dunaevsky (1990, Tribol. Trans.33(1), pp. 33–40) and provides their correct expression. The subject has strong practical significance in the field of piston engines and compressors, and it is currently getting additional prominence due to stringent emission regulations. The bounds stem from an earlier version, developed by the authors using a semi-empirical approach, and published in the 1970s in Russian technical journals. A semi-empirical background of the bounds was inadvertently missed in the aforementioned Tribology Transactions’ publication. This fact, and the virtual inaccessibility of Russian sources to the English reader, interfere with the proper use of the bounds and cloud their authorship. In this technical brief, the correct expression of these conformability bounds, the development process, and uses are highlighted.