Common used bolts size for bicycle (Titanium):
M5*9 :for front Derailleur, Rear Derailleur etc
M5*10 :for fixing bottle cage , disc-Brake , Rear Derailleur etc
M5*12 :for fixing bottle cage , disc-Brake etc
M5*18 :for fixing front Derailleur , fixing seat post, Clamps Stems etc
M5*20 :for Brake lever , Derailleur etc
M5*40 :for Seat post etc
M6*10 :for V brake etc
M6*12 :for V brake etc
M6*16 :for Thumb Shifter, Brake Lever etc
M6*19 :for Crank Only, Stem
M6*20 :for Brake lever ,Derailleur , Stems etc
M6*25 :for V brake, handlebar etc
M6*30 :for seat post, Headsets etc
M6*35 :for seat post etc
M6*40 :for Stems, seat post etc
M8*18 :for head tube etc
M8 :for V brake, Forks etc
M10 :for V brake, Rear Forks, fold bike etc