Good holdfast but may need to be roughed up to work
Initially when I bought a pair I was disappointed because they didn’t hold in my 3inch thick top. I was able to make them work by roughing up the surface with 60grit sandpaper in a CIRCULAR motion around the shaft. Doing this increased the grip and they now work very well. It took all of 5 minutes to do this.  Photo is a before and after.
Rating: 4 stars