Abstract: An improved cooling system for electronic assemblies provides cold bars (10) and cold plates (60) for supporting and conducting heat away from a plurality of electronic assemblies (12, 52) attached thereto. A plurality of refrigerant holes (A-F, 70-77) are drilled through the cold bar or plate. End caps (27, 28, 61, 62) have well-like areas forming refrigerant return passages that cooperate with the cold bar or plate to interconnect individual refrigerant holes or groups of holes to form multiple pass refrigerant paths through the cold bar or plate to external connections for connecting to a refrigeration system. The holes are preferably threaded to improve heat transfer characteristics. The pattern, sizing, and grouping of holes can be varied to adjust the design of a particular cold bar or plate to the heat load of a given application.