Why not just get a nice set of metric hex keys, or hex sockets? You will use them in the future. From memory, I want to say that the size that you need is 4mm, but 5mm, 6mm are also popular hardware sizes.
4mm, 3/8" drive bits are too big you need 1/4" drive or long Allen wrenches. Snap on makes a fantastic 1/4" drive hex socket set but very expensive. Here's a couple cheap and easy options~ ratcheting screwdriver with interchangeable bits or a 1/4 ratchet with a long extension and a bit holder socket.