Patent ID: 6988712

Claim:
A screw jack comprising a case body, a guiding inner cylinder part vertically disposed at said case body, a rotatable cylinder, a threaded cylinder and a center threaded rod which are sequentially inserted in the inner side of said guiding cylinder part, said rotatable cylinder including an inner periphery thread and an outwardly facing flange-like large bevel gear disposed at a lower end part of said rotatable cylinder, said large bevel gear being engaged with a small bevel gear borne by said case body, a thrust bearing being sandwiched between said large bevel gear and a bottom plate of said case body, said threaded cylinder being provided with an outer periphery thread which is to be engaged with said inner periphery thread of said rotatable cylinder, and an inner periphery thread, said center threaded rod being provided with an outer periphery thread which is to be engaged with said inner periphery thread of said threaded cylinder, an upper end surface of said center threaded rod being provided with an engagement part which is to be engaged with a jack attachment part of a body to be lifted up such as an automobile, said small bevel gear being rotationally driven from outside to rotate said rotatable cylinder through said large bevel gear, thereby causing said threaded cylinder and said center threaded rod, which are mutually threadingly engaged and transmitted, to be extended upward and contracted downward and wherein said engagement part of said center threaded rod is constructed such that when said engagement part is in engagement with said jack attachment part of said body to be lifted up such as an automobile, said center threaded rod provided with said engagement part is prevented from being rotationally driven.