Pretty sweet little hot shoe adapters allow you to add extra accessory mounts to your DSLR rigs without tools. There's another version of this adapter that has a nice female insert if you're trying to mount in onto a male stud. (Excuse that last sentence if it sounded a bit mature).
The knob below allows you to tighten or loosen and relocate as you please without carrying a spare driver tool. There's slighty cheaper 'cold shoe' mounts available, but price is about average on this one and a cool addition to your DSLR Cages or Accessory Brackets.