The Coldshoe Lock works with the Half Cage Rail to lock your DSLR camera firmly in place. It screws onto the Z-rail at the top of the Half cage Rail via two 5/32nd allen keys. The other end of the Coldshoe Lock slides into the hotshoe of the camera locking the it firmly in place.This prevents the camera from rocking when engaged with a follow focus. Note: If you already have a Half Cage Rail and want to use it with the ColdShoe lock, please email sales@zacuto.com to make sure your model is compatible.