Available in UNC threads with sizes from ¼–1 in. in 1/16 in. increments, HARDLOCK Nuts have all-metal construction and can be used repeatedly while maintaining loosening prevention effect. Structure prevents loosening by combining centered concave top nut and off-centered (eccentric) convex lower nut to form wedge when tightened. This applies force perpendicular to bolt, and when top and bottom nuts are tightened, self-locking force of wedge prevents loosening.
This story is related to the following:Metal Nuts | Self-Locking Nuts