Abstract: A self-tapping screw type fastener of the present invention is characterized in that an external thread 7 of an adjusting rod (self-tapping screw) 5 is screwed into and fastened to an output rod 1 with tapping an internal thread 3 in an inner peripheral surface of a smooth prepared hole 2 of the output rod 1. The adjusting rod 5 has a threaded shaft 13 with the external thread 7 formed thereon and a smooth guide shaft 14 projecting from an end of the threaded shaft 13. The outer diameter R1 of the smooth guide shaft 14 is set to be smaller than the major diameter R4 of the external thread 7 and to be slightly larger than the minor diameter R2 of the external thread 7 or the minor diameter R3 of the internal thread 3. Because of the diameter difference “t” between the diameter R1 and the diameter R2 or R3, a step 20 is formed so that the step comes in contact with the nearest ridge of the internal thread 3, thereby preventing the adjusting rod 5 from getting loose.

Abstract: A booster 3 has a structure that a return valve 14 is formed into a two-step throttle incorporating a first throttle valve 36 and a second throttle valve 37 formed continuously from the first throttle valve 36. When a valve spool 28 has been moved forwards when the operation is performed, a gap of the first throttle valve 36 is reduced. Also a gap of the second throttle valve 37 is reduced. Therefore, hydraulic fluid discharged from a pump is passed through an inlet passage 12, and then introduced into the second annular groove 13. Then, the hydraulic fluid is throttled by the first throttle valve 36, and then throttled by the second throttle valve 37. That is, the hydraulic fluid is throttled in the two-step throttling manner. As a result of the two-step throttling structure, the overall velocity of the flow of the hydraulic fluid can smoothly be changed without rapid change. Therefore, fluid flow noise caused from the change in the velocity of the flow can be prevented.

Abstract: A housing is provided with a guide which projects into a cylindrical section of a power piston. A reaction piston is slidably supported by the guide, and an input shaft is in turn slidably supported by the reaction piston. A spring which urges the reaction piston is disposed in a clearance defined between the outer periphery of the guide and the inner periphery of the cylindrical section of the power piston. A first engaging portion is formed on the reaction piston to project radially outward, and a first stop is formed on the cylindrical section to restrict a rearward movement of the reaction piston. A second engaging portion is formed on the input shaft so as to project radially outward while a second stop is formed on the reaction piston to restrict a rearward movement thereof. With this arrangement, an increase in the axial and the diametrical dimension of a liquid pressure booster can be prevented.