Abstract: A rack boot which is installed at the steering rack portion of an automobile comprises a small-diameter ring portion, a large-diameter ring portion, and a bellows portion interposed between the small-diameter portion and the large-diameter portion. An angle to an axial line of the boot of a slanted wall of a first crest in the bellows portion is arranged to be 70.degree. to 85.degree., whereby the slanted wall is turned in when the boot contracts to an extreme extent. As a result, the shrinkage ratio of the boot in the axial direction can be increased without any necessity to enlarge the outer diameter of the crest portion of the boot or to increase the number of crests. Consequently, the size of the rack boot can be reduced.

Abstract: Plastic dust-proof boots which are made of thermoplastic resin by means of blow molding and provided at least on one end of a bellows with a stationary ring to be fitted to an engaging groove formed on an attaching shaft and methods for manufacturing the plastic boots. In the boots, an inner circumference base upright wall of the stationary ring is formed at a nearly vertical state, and the inner circumference base upright wall of the stationary ring is connected through a sleeve having an inner diameter so that the attaching shaft can be loosely fitted. In manufacturing the boots, the stationary ring and the sleeve are molded during the parison molding previously or during mold tightening at the blow molding stage, and the blow molding is performed while the stationary ring and the sleeve are grasped between molds.

Abstract: A dust boot for a universal joint covering two joint elements having largely curved corner portions in the outer peripheral surface thereof near their joint portion, comprises a resilient annular covering portion for covering the joint portion of the universal joint and two annular end portions which are integrally formed with the covering portion in axially both ends thereof. The annular end portions are mounted on the two joint elements near their joint portion. Since the area of an open end of the dust boot mounted on the joint element having largely curved corner portions is made smaller than the cross sectional area of the outer peripheral surface of the joint element, specifically only the curvature of the open end of the dust boot corresponding to the largely curved corner portions of the joint element is made smaller than that of the corner portions of the joint element, the dust boot can be closely mounted on the joint element with excellent sealing effect.