The hinge-stiff rig is a two-piece rig that connects the lead to the bait via stiff line material.
The bait is a pop-up style item and is attached tightly to the hook, and the hook is mounted on a short length of line to a swivel or ring that in turn is attached to the boom section which then connects to the main line and the lead. The point where the boom connects to the hook section is weighed down to counter the uplift of the pop-up bait.
The rig is credited with numerous superb catches and its proponents claim it deters smaller fish.
Here are some links to useful articles about hinge-stiff rigs on external webpages:
How to tie a hinged stiff rig at carpfeed.com
How to tie the perfect hinged stiff rig at carpology
VIDEOS:
Watch videos about hinge-stiff rigs-