So I need a 29.8mm seat tube clamp with braze-ons for a bike rack. Only one company makes such a thing in that diameter, but the clamp itself looks rather flimsy. Two or three other companies make much sturdier-looking clamps but only in 31.8mm and 34.9mm (2 or 5 mm too big). I found a seat tube shim to increase the outer tube diameter from 29.8 to 34.9, but I can't find any to convert from 29.8 to 31.8. I have two options:
1) Buy the bigger 34.9mm clamp and the 5mm thick shim to go with it
2) Buy the smaller 31.8mm clamp and try to find a 2mm thick piece of metal to make my own shim.
Is either one of these a better idea than the other?