Fixed-moment nut

A fixed-moment nut includes a pull rod, a large retainer, a hollow handle with a pit at the front end, a plug cover, a large steel ball, a gasket, a small retainer, a small steel ball, a bush, a spring and a flat nut, wherein the large steel ball is mounted between the pull rod and the pint at the front end of the hollow handle through the large retainer; the small steel ball is mounted between the gasket and the bush through the small retainer; the pull rod is sleeved by the spring arranged inside the hollow handle; one end of the spring is propped against the bush, and the other end is propped against the flat nut; the flat nut is mounted at the tail end of the pull rod through threads; and the plug cover is mounted at the tail end of the hollow handle. The utility model has the advantage of solving the problem that measured parts suffer from different compression forces during the mounting and clamping processes and cause different measurement results. The manufacturing cost is low, the use is convenient,