Oil filter

1. An oil filter comprising:

a casing including a cylinder portion with an opening in one end of the casing, a threaded portion disposed on an inner peripheral surface of the cylinder portion; and

a cap threadably engaging with the threaded portion and containing a filter element between the casing and the cap,

wherein the cap includes: a flange abutted on an open end surface of the cylinder portion of the casing and allowing the cap to be positioned by the casing; and a recess fittably receiving a sealing member in a normal mounting position for obstructing oil flow between the cap and the casing, and

the cap includes at least one facilitating portion that allows at least a part of the sealing member to move onto a radial end surface of the flange when the sealing member is mounted erroneously on an outer peripheral surface of the cap at a place between the flange and the recess and the cap is positioned by the casing;

wherein the at least one facilitating portion is at least a part of the flange that is set in a radial length along which the movement of the sealing member is facilitated, and

the at least one facilitating portion comprises a projection having a smooth curved surface, the projection connects, via the smooth curved surface, an outer peripheral surface of the cap to a side surface of the flange that adjoins the recess.

2. The oil filter according to claim 1 ,

wherein the projection is disposed on the outer peripheral surface of the cap at the place between the flange and the recess and is unitarily disposed with a surface of the flange which adjoins the recess.

3. The oil filter according to claim 1 ,

wherein the at least one facilitating portion comprises a plurality of facilitating portions that are disposed at a plurality of circumferential places in substantially symmetrical relation with respect to the center axis of the oil filter.

4. The oil filter according to claim 1 ,

wherein the at least one facilitating portion is a flat surface parallel to the center axis of the oil filter on an outside surface of the flange in the radial direction of the cap.

5. The oil filter according to claim 1 ,

wherein the at least one facilitating portion comprises at least one first facilitating portion and at least one second facilitating portion; and

the at least one first facilitating portion comprises the projection that is unitarily disposed with a surface of the flange which adjoins the recess,

the at least one second facilitating portion comprises at least a part of the flange that is disposed in a radial length along which the sealing member moves when the sealing member is mounted erroneously, and

the at least one first facilitating portion is disposed at a position substantially the same as the at least one second facilitating portion in the circumferential direction of the flange.

6. The oil filter according to claim 5 ,

wherein the at least one second facilitating portion comprises second facilitating portions that are disposed at a plurality of circumferential places substantially in symmetrical relation with respect to the center axis of the oil filter.

7. The oil filter according to claim 5 ,

wherein the at least one second facilitating portion is a flat surface parallel to the center axis of the oil filter on an outside surface of the flange in a radial direction of the cap.

8. The oil filter according to claim 1 ,

wherein the flange and the recess are spaced away from each other in an axial direction of the oil filter.