This Aerospace Standard covers components of rotary flap assemblies, assembled by peening processors, to be used with portable equipment for peening of metal parts. Flap assemblies are used for rotary flap peening, a portable method used to induce surface compressive stresses in metal parts as detailed in AMS2590. The tool flaps are rotated rapidly and manually forced against a substrate being peened. A portion of the flat face of each flap embedded with shot strikes the metal surface causing peening .