23.75" H-Channel Section to connect AX Height Extenders to CSP, All ClearSonic Panel systems feature a low-profile, heavy duty "mechanical lock" full-length hinge that is the best in the industry. ClearSonic Panels go through an extra step in the manufacturing process that creates a "locking groove" on the long edge of the panel. This locking groove accommodates a hard tooth on the inside of our proprietary hinge that snaps into the groove for a superior, longer lasting hold. Some use the inferior "friction-hold" hinge that uses flexible barbs and friction to hold onto the shields. Friction-hold hinge must be applied with force and will only stay in place as long as the hinge opening is smaller than the panel thickness. The problem is, plastic has a memory and over time will open up under the stress. Once the hinge opens up, it no longer will hold tight and will start to pop off more and more frequently. They know. They used friction-hold hinge until early 2000. At that point they made the decision that this style of hinge was not durable enough to be used on the industry standard ClearSonic Panels. They want their systems to perform for years, not just months.