A keychain I made for holding two small scredriver bits, a flat and a philips. The bits stay in place using friction, so they need a considerable amount of force to fit, I even used a clamp to do that. 

The hex holes are 4.5mm from vertex to opposite vertex or about 3.9mm from side to opposite side, the bits are about 28mm in length, consider this if you want to make it.

I also leave here the sldprt in case you want to modify the model. The letters in the printed model didn't come out great, so I removed them from the files.