Exactly as the title suggests, the smallest keychain bit driver I could make while still being able to open highly tightened screws.

I have yet to encounter a screw I didn't manage to open with it (even impact driver tightened ones. Use high quality bits for those otherwise it will skip)

While there are plenty of other keychain bit drivers non are this small. 

I tried many of them but all were too big and uncomfortable which led me to design this one and its on my keychain since.

Press fit design for one ¼-inch bit (not a permanent fit)
Wing span of 32mm (1.25") and standing 17mm (0.67") tall,
weighing 2 grams and can be in your hands after just 15min of print time

(step file included for easy remixing)