Just found a tiny metal ball in my bike fiddling corner. I haven't worked on any ball bearing since the last cleaning, so I'm a bit confused where it might have dropped out of. It's pretty exactly 3mm in diameter. Is there any chance to infer which ball bearing it may have dropped out of at some point?
Pedals usually have 1/8". Depending on how you measured the diameter, maybe that's what you found. I think you'd notice fairly significant play in the pedal for a ball to have fallen out though.
You can always start with Sheldon for some ideas of what bearings are used where, 1/8” includes pedals, headsets, freewheels. Watch out for obsolescence tho. Freewheel might imply freehubs too.
Sealed/cartridge bearings can have some pretty small bearings in too and they can be found all over bikes. However, I think you would know if you’d taken something like that apart and spilled the bearings.
Short of taking the likely suspects apart to check, I’m not sure of the value in inferring where it’s from - it could be from somewhere else completely anyway!