a method and apparatus for molding casing halves of a magnetic tape cassette in which one or more - windows in the casing half are firmly retained by remaining portions thereof regardless of the solubility of the two plastic materials employed or other molding conditions . the window is formed with a projecting edge portion which extends well into the plastic of the remaining portions of the casing half . in one embodiment , the window is molded first and then the remaining portions are molded around the edge portions of the window . in another embodiment , the other portions are molded first using slidable cores to define the window portions , and then the windows are molded .