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 mechanical shaft joint boot integrally made up of a large-diameter ring portion and a small-diameter ring portion with a bellows portion interposed therebetween, and a straight portion connecting the bellows portion with the large-diameter ring portion. The distance 11 between the large-diameter ring portion and the small-diameter ring portion is smaller than the distance l2 between a large-diameter ring mounting portion and a small-diameter ring mounting portion of the joint, and the outside diameter of a first crest of the bellows portion is not larger than the inside diameter of the straight portion. Accordingly, when a shaft of the joint inclines to cause inclination on one side of the boot, a surface pressure being imposed on the first crest is not increased correspondingly, thereby suppressing its wear and enhancing service time of the boot.

Abstract: A boot with a bellows interposed between a large-diameter ring and a small-diameter ring is disclosed. In the bellows, the crest which is the closest to the small-diameter ring is made thinner than the other crests. Accordingly, when the boot is mounted on a mechanical shaft joint, the crest closest to the small-diameter ring is folded preferentially, so that the pitches of the other crests are maintained. The other crests are not brought into contact with each other during the cross movement of the mechanical shaft joint or even if they come into contact with each other, the contact pressure reduced, and the durability is thereby enhanced.

Abstract: A mechanical shaft joint boot made of a resin comprises a bellows having four to seven crests between a large-diameter ring and a small-diameter ring, in which a crest excluding the first crest between the large-diameter ring and the center of the bellows has the maximum top curvature radius. By providing this structure, the thicknesses of these crests are made uniform and elongation-compression distortion is restrained from being concentrated at their tops. The widening of the tops of the crests also restrains any kinking phenomenon which may be produced. Therefore, the durability of the tops of these crests is increased and the durability of the boot as a whole is hence also increased.

Abstract: A mechanical shaft joint boot of a polymeric elastomer is provided with bellows between a large-diameter ring and a small-diameter ring, a first crest of the bellows being formed between the large-diameter ring the small-diameter ring after the first trough and a second trough being formed so as to have a smaller apical diameter than that of the first trough, and a circumferential convex strip is formed on the sidewardly inclined surface of the first crest on the inner side of the first trough and/or on the respectively opposed inside surface of the second trough. Therefore, the second trough is pushed toward the side of the small-diameter ring and is not held between the first trough and the driving shaft on the compressed side during a crossing movement, which reduces the compression distortion and increases the durability of the boot.

Abstract: A boot for a universal joint, which is made of a high-molecular elastomer, in which bellows having three or more ridges are extended between a larger and a smaller ring portion, and in which a valley is formed between the first ridge from the larger side of the bellows and the larger ring portion. In this boot, the crest of the first ridge has its inner circumference located outside of the imaginary circumference of the frustum of a cone, which is formed by joining the end portion of the larger ring portion at the side to be connected to the bellows and the crest of the second ridge. As a result, the wears of the ridges (especially of the first ridge) due to their mutual contacts are not promoted so that the boot can have its durability improved.

Abstract: A dust boot for a constant velocity universal joint has a bellows-shaped boot made of chloroprene-rubber substantially excluding wax and a polyamide resin coating layer having excellent wear resistance, which is formed on the outer surface of the bellows-shaped boot without peeling. Between the coating layer and the polyamide resin boot is formed a primer layer made of a mixture of chloroprene-rubber and isocyanate compound so that the coating layer does not peel off from the bellow-shaped boot.

Abstract: A semicircular packing comprising a metallic portion and an elastic portion sealing the pierced hole of the cylinder head when setting, having thick portions at both ends of auricules and a thin portion between thick portions at both ends, at least on the metallic portion partly contacting with the outer surface of the pierced hole. This semicircular packing is easily conformed to the curved peripheral surface of the pierced hole and makes it unnecessary to coat it with sealing liquid as well as able to permit the clamping torque of the cylinder head to be small and yet maintain its sealing state over a long term of years without being subjected to excessive or premature aging.

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.