I ordered the extension kit with the outdoor umbrella clamp to accomodate my railing. I have a railing system that is composite-based, from Timber Tech. It is neither completely rounded, nor completely square along the rail. The extension kit definitely made it possible for me to use the RailEZ clamp, however I found a couple of issues: 1) The instructions to change out the “plastic pads” was a bit tricky, but I succeeded. 2) The hard “ plastic pads” have zero grip on a composite rail. It’s like putting ice on ice. Slippery on slippery. So even with pressure, the clamp was difficult to get completely secure. I eventually got into an exact position that allowed me to feel confident that my umbrella wouldn’t rotate off the railing with wind. However, to assist, I also added the bottom clamp to the bottom rail. This clamp also has plastic pads that have zero grip. No matter how tight you squeeze them on to the bottom rail. So I ended up using zip ties to hold the base clamp with the bottom of the pole in place. What this means is that once I put that umbrella up, I am not moving it. Ever. So while it works great, I do not have the flexibility of moving the umbrella as easily as shown in the ads. In the end, I am happy with it, because I had no other options with this railing system, so do appreciate the extension kit was available. Thank you.