This is an original factory replacement part. Factory replacement parts are manufactured to the exact same specifications and tolerances and use the same manufacturing materials as the original parts which guarantees excellent fit and reliable operation. Disassembly and assembly may be required to replace part while some parts may require installation by a qualified gunsmith.NoteHammer only. Requires the following items to complete the hammer assembly:Hammer Plunger - 266558Hammer Plunger Spring - 515784Hammer Plunger Cross Pin - 583700