From the largest watch movements to the smallest, these screwdrivers will do them all... With some modifications, at least.
Our screwdriver set includes drivers as wide as 2.50 mm and as small as 0.60 mm. I have yet to use anything smaller than 1.00 mm, but it's coming.
The primary fasteners in watch movements are screws—regular flathead screws. Phillips screws have no real place in watches, and Torx? Forget it.
Having the right-sized screwdriver is critical for these little screws, since even a small slip can damage the slot or the blueing. When it comes to high-end watch movements, no damage is acceptable. A good rule of thumb is that your screwdriver bit should be about 90-95% as wide as the screw head. This should allow a secure hold, while minimizing the risk of damage to the screw hole (if the screw is countersunk).
The smallest screwdrivers have some secondary uses as well. We use the 0.60 mm bit to transfer the lightest oils from the bottle to our oil cups, and they can be used as depth gauges for micromechanics as well.
As with all tools, you shouldn't cheap out on your screwdrivers. Misshapen tips can be modified, but poor quality steel will just be a headache. It's impossible to see in these photos, but the heads of each screwdriver in our set rotate on ball bearings, making them a true delight to use.
Watchmaking student at the Lititz Watch Technicum, formerly a radio and TV newswriter in Chicago.