Patent ID: 6991062

Claim:
A ball screw comprising a screw shaft having a thread groove in the outer periphery thereof, a nut having a thread groove in the inner periphery thereof opposed to said screw shaft, and a plurality of balls disposed in a rolling way defined between said thread groove in said screw shaft and said thread groove in said nut, wherein a fitting surface engaging a support member with a direct contact for supporting said nut fitted therein is formed on the outer peripheral surface of the nut in the axial middle region of said rolling way and non-fitting surfaces that do not contact said support member are formed on the outer peripheral surface of the nut on the opposite axial sides of said rolling way, wherein the axial middle region includes a center point of the nut, wherein the fitting surface and the non-fitting surfaces of the nut are smoothly joined as a smooth convex surface, wherein said non-fitting surfaces extend over a distance of at least one lead axially inward from the two opposite axial ends of said rolling way.