The Pinion C1.12 - 4130 Steel bridge is purpose built for the C1.12 drive-train. Weld or Braze only. This Pinion C1.12 - 4130 Steel bridge uses a preformed sand cast mold, making it compatible with other frames that use 4130 Steel . This product is to be installed by experienced master level frame builders and master level welders of aluminum only. The bottom bracket features filleted reinforcements for an ultra light and convenient fit of the pinion gear box. If you are a master frame builder or master of welding aluminum this product could be for you. There is no guarantee it will fit so use the contact form if you have any questions. Retrofitting is not recommended.