Disc brake and piston boot

1. A disc brake comprising:

a piston that presses at least one of a pair of pads facing each other against both surfaces of a disc;

a cylinder that accommodates the piston to be movable and has a bore of which one end opens so that a tip of the piston protrudes; and

a piston boot that is disposed between a tip side of the piston and the cylinder and has a stretchable part capable of expanding and contracting with the movement of the piston,

wherein the piston boot has an annular fixing part that is formed on one end side of the stretchable part and abuts against an inner peripheral side of the cylinder, wherein an outer peripheral surface of the annular fixing part is provided with a first region that abuts against an inner peripheral surface of the cylinder, and a second region that is disposed closer to a bottom side of the cylinder than the first region in a piston axial direction,

wherein an outer diameter of the first region is larger than an inner diameter of a region of the inner peripheral surface of the cylinder that faces the second region, and

wherein in the inner peripheral surface of the cylinder, an inner diameter of a third region abutting against the first region is larger than an inner diameter of a fourth region abutting against the second region.

2. The disc brake according to claim 1 ,

wherein the piston boot has an enlarged diameter region having a larger outer diameter than any of the first region and the second region between the first region and the second region, and

wherein the enlarged diameter region fits into a peripheral groove formed on the inner peripheral side of the cylinder.

3. The disc brake according to claim 2 ,

wherein in the piston boot, the stretchable part is coupled to the fixing part on an opening side of the cylinder.

4. The disc brake according to claim 1 ,

wherein in the piston boot, the stretchable part is coupled to the fixing part on an opening side of the cylinder.

5. The disc brake according to claim 1 ,

wherein an annular stepped part on which the fixing part is disposed is formed on an opening side of the bore, and wherein the stepped part has an inner peripheral surface against which the outer peripheral surface of the fixing part abuts, and an annular wall surface that faces one annular facing lateral surface of the fixing part and is located on the bottom side of the cylinder, and

wherein the second region of the fixing part abuts against the inner peripheral surface of the stepped part when the fixing part is disposed on the stepped part and the facing lateral surface abuts against the wall surface.

6. The disc brake according to claim 5 ,

wherein the piston boot has an enlarged diameter region having a larger outer diameter than any of the first region and the second region between the first region and the second region, and

wherein the enlarged diameter region fits into a peripheral groove formed in the inner peripheral surface of the stepped part.

7. The disc brake according to claim 5 ,

wherein a largest outer diameter part of the enlarged diameter region is shifted from a central position between the facing lateral surface and an opposite lateral surface opposite to the facing lateral surface in the fixing part.

8. The disc brake according to claim 7 ,

wherein in the piston boot, the stretchable part extends from an opposite lateral surface of the fixing part opposite to the facing lateral surface.

9. The disc brake according to claim 6 ,

wherein in the piston boot, the stretchable part extends from an opposite lateral surface of the fixing part opposite to the facing lateral surface.

10. The disc brake according to claim 5 ,

wherein in the piston boot, the stretchable part extends from an opposite lateral surface of the fixing part opposite to the facing lateral surface.

11. The disc brake according to claim 1 ,

wherein the piston boot has an enlarged diameter region having a larger outer diameter than any of the first region and the second region between the first region and the second region, and

wherein the inner peripheral surface of the cylinder has a peripheral groove having a larger inner diameter than any of the third region and the fourth region between the third region and the fourth region.