a assembly of mated molded parts and a method for making same are disclosed in which the assembly has first and second parts with precisely mating surfaces . the first part is formed by molding , casting , or the like such that the mating surface of the first part is formed with at least one protrusion . the second part is formed in place against the first part such precisely mating surfaces are formed with the second part enveloping the protrusion . the two parts thus formed are forced apart from each other . the protrusion may be formed with a head which interlocks with the second part . when the parts are separated , the head breaks from the protrusion . in a particular embodiment , a bearing cap is disclosed having a central opening for the passage of a shaft .