The other night I needed to change a traction tire on my Big Boy, so i went to my precession tool kit to get a nut driver to, but the smallest one I had was a 3mm driver and the Big Boy has a 2.5 mm bolts holding the connecting rods to the drivers.
So what to do,
1. use needle nose pliers and strip the head of the bolt, no
2. by a $30us precessing tool kit on line and wait a week for it to show up. no
3. search hardware stores, electronic shops and hope I find a driver, already did that and the smallest one I had found was 3mm. so no

The only tools that I had that were that small were Hex keys or allen keys. Wait a second if a 2.5mm hex key fits a into a 2.5mm socket cap screw then I should have a 2.5 mm socket.

So here it is a 2.5mm nut driver that cost less than 4 for a $1