| 摘要 |
<p>For being slidably inserted into a cylinder bore defined by a cylindrical surface extending in a predetermined direction, a piston (8) has a head portion (81) extending perpendicular to the predetermined direction and a barrel portion (82) connected to the head portion. The head portion has an outer circumferential portion which is close to the cylindrical surface when the piston is inserted in the cylinder bore. The barrel portion has at least three wall portions (82a, 82b, 82c) which are extended from the outer circumferential portion in the predetermined direction. The wall portions are arranged in a circumferential direction to form a substantially cylindrical shape in cooperation with one another. <IMAGE></p> |
