Everyone claims the Williams and the Snapon are the exact same tool, well unfortunately the original model fit my williams driver perfectly but didn't fit the snap on at all. 

I added some reliefs so the bit holder can fit into the cap properly, shortened it, removed some material from the bit retainer, and extended the length of the retainer. The snapon's internal space is less cylindrical than the williams so it's not perfect, but it works and can still hold 6 bits!

This was my first (successfulish) attempt at modifying a part, huge thank you to the original creator for a neat idea!