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Free running locking fasteners assemble similarly to standard fasteners without any locking features until seated. At this point, the resistance to loosening is obtained by an additional accessory device, which may or may not be preload-dependent. Prevailing torque locking fasteners require additional torque to assemble and disassemble because of distorted threads or various other features. Prevailing torque is defined as the torque required to turn such fasteners with zero preload. Chemical locking is accomplished by causing a chemical reaction, with FIGURE 53 Using lock wire to secure bolts. (Adapted from Bickford, 1995.) adhesives or corrosion, that increases thread friction. The next four subsections describe locking fasteners and techniques in the four groups.