SRAM Braze-on Adaptor Wide Spacing (47.5 Chainline) 31.8 with Chainspotter Stop:

Sram:

SRAM front derailleur braze-on clamp adapter is designed to work with the SRAM front derailleur and includes a flush side to correctly hold the derailleur as well as a lip that provides a backing for the chain catcher screw, with chains potter stop. Size: 31.8 mm.