I bought 3 of these when I was building a 7" x 9" x 74" box girder mantle. I used a carpenter's machine to align everything, glue it together, and then used it to keep the pressure even throughout the night (I also used 2 pipe clamps as well. They did a great job. Not only did they hold tight enough, but they didn't mark or dent the wood. Friction. At $12, they're great for small projects. They hold tight, but don't expect the same holding power as an $80 metal clip.