C.F. Theodor Steinweg receives the United States patent # 81,306 to “metallic action-frame secured directly to the pin block in “an upright or other piano- forte” and composed of metallic hangers provided with holes to receive the metal traverses”: “By these improvements an action […] is so constructed that all the parts can be readily interchanged, and each action frame can be inserted into every piano-forte of the same class without requiring any fitting”. The action, constructed in that way, has become a single module that can be inserted into a piano or removed from it, fixed or completely replaced, if necessary – without the need to send the entire piano to the factory for any of the action repairs. This very idea of the modular construction, applied to pianomaking, is the sign of C.F. Theodor Steinweg’s brilliant engineering mind. This is his first patent, followed by many more.