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https://si.shimano.com/en/pdfs/dm/GAFD001/DM-GAFD001-01-ENG.pdf
"Installing the support plate
If installing the front derailleur to a brazed-on type frame, a support plate must be attached tothe seat tube.
Be sure to install this in order to prevent damage to the frame from the pressure of the front
derailleur support screw.
"(I just googled "shimano grx front tab" and looked for a suitable result.)
What is this tab that came with a Grx front derailleur?
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