The 3M roto peen mandrel grips small flaps containing captive shot for peening of fine tolerance metals components. For use with flap assembly, we offer three sizes for internal diameters and flat surfaces. We engineered our 3M roto peen mandrel to deliver quick, efficient repair and maintenance to us army helicopters to components like rotors and rotor hubs in the field, our 3M roto peen mandrel and its associated flap assembly allowed peening action using a die grinder or disc sander. In the early 1970s, the 3M roto peen flap assembly (or TC 330) was qualified and written into military specifications. It soon spread to other aerospace applications. Used today primarily for aerospace applications, the mandrel comported with a flap assembly allows use of a die grinder or disc sander to perform captive shot peening to repair metal surfaces. The assembly consists of tungsten carbide shot bonded to a flexible polymeric flap gripped by the mandrels attached to the power tool. The spinning flap is held near the surface so that the captive shot hammers the metal surface with each revolution. Our 3M flap/mandrel assemblies provide convenient portability and are especially effective for precision in service rework manufacturing, repair of small areas and peening holes with diameters down to 1/2 in. Flaps can also be cut with scissors to peen confined areas or peen into areas with a radius down to 1/16 in. Captive shot peening is used for repair or limited access work or when free shot cannot be tolerated. Having the shot used to peen metal surfaces in a captive flap allows for more control and greater access to areas that require this strengthening procedure. Evolved from the days of blacksmiths hammering swords, peening is a process that utilizes compressive surface stress to strengthen metals, improving resistance to fatigue fracture and stress corrosion cracking. The aerospace industry has stringent peening specifications, in which adherence must frequently be documented. Off-spec peening can result in the failure of parts. 3M also provides almen gauges to provide precise readings of strip deflections to measure peening intensities. Adopted by the SAE (Society of automotive engineers), the almen scale of peen intensity measures the curvature of a standardized steel strip when peened on 1-side.