Peening with metallic shot or glass beads is intended to induce surface compressive stresses in metal parts such as axles, springs (helical, torsional and leaf), gears, shafting, aircraft landing gear assemblies, wing structures, jet engine support members, helicopter rotor hub assemblies, etc. which are subjected to repeated applications of load pattern for the purpose of improving resistance to fatigue and stress corrosion cracking. Metallic shot peening is also used for applications such as to close porosity in castings and to straighten or form applicable parts. Peening with glass beads, is used primarily where contamination presents a special problem, where a fine surface finish is required, or when peening in a very sharp radius, such as a thread root, is required.