A latch bolt mechanism for tilting window sashes includes an actuating spring that is integrally molded of plastic material in one piece with the latch bolt. The spring has a transversely corrugated configuration, comprised of at least two transversely disposed wave-like spring sections. Each spring section includes a pair of oppositely oriented U-shaped sections having spaced apart semi-cylindrical portions at opposite sides joined by transverse connecting sections. In a relaxed configuration of the spring, the several connecting sections are substantially parallel to each other and are longitudinally spaced apart. In a compressed configuration of the spring the connecting elements lie at an angle to each other and the several semi-cylindrical portions are closely spaced or in contact providing for the required spring compression without excessively stressing the plastic material. Significant production economies are realized with the one-piece, molded construction of the latch bolt and spring.