Originally Posted by
FNoordman
Guys, gotta help me out here… I bought another bottle holder for my Trek. But I noticed that there is even space for something on the bottom side of the frame (red arrows on pic). It's actually the same screws as for bottle holders, but I can't imagine why you would put one there (doesn't even fit I think). So anyone a clue what this is for?
Touring bikes often have three bottle cage mounts...one under the down tube like you show on yours. Here's a good example:
Vintage Touring Bike Restoration - BIKEPACKING.com
What model is your Trek?