The 3M roto peen assembly kit contains the components needed for captive shot peening, repair or maintenance of metal parts. Each kit includes a roto peen almen strip holder, TC-330 roto peen flap assemblies in two sizes (9/16 x 1-1/4 in and 1 x 2 in) and roto peen mandrels 7210 and 7211. This kit does not include the almen strips, die grinder, almen gauges or other measurement equipment. The 3M roto peen assembly kit delivers the parts necessary to work on a range of sizes, geometries, applications. This allows users to complete peening tasks, primarily in the aerospace industry, without the use of large, stationary equipment. Combined with the correct tools, 3M roto peen assembly kit can help you with peening after grinding, before plating, forming and straightening, bond testing and more. Used extensively for production, maintenance and repair in the aerospace industry, captive shot peening imparts residual compressive stress into the surface of metals by hurling shot against the metal like a small hammer. This compressive surface stress strengthens the material, improving resistance to fatigue fracture and stress corrosion cracking. Captive shot peening is a quick, portable and cost effective method of aerospace production and repair. To create the unique and portable assemblies included in this kit, durable tungsten carbide shot is adhered to flexible polymeric flaps using high strength resin, which helps resist damage and heat from consistent use. The flaps are secured by a mandrel designed specifically for this application. The flap/mandrel assembly can then be placed in the collet of a rotary tool designed to run at the appropriate rpm for the needed intensity.