Strong strap padded with vinyl tubing with control bar attachments at each end. One end has quick release for emergencies. The "U" shape created allows you to hook into a harness hook.  Also called a "D-loop" since it forms a "D" shape  when attached to the bar.  Newer units have a red plastic ball to pull on for the safety release instead of the red fabric loop pictured.

Note: Hooking into a kite can be dangerous. This is recommended for experienced riders only.