and they have been very sturdy and the table does not slide when he bumps ...
I purchased these to raise my tall and aging father's table. These risers helped bring the table to a useable  height for him (I also purchased a higher chair to use with the raised table).  He has the table on a hardwood floor.  The risers are made of hard plastic and I was a bit skeptical that they would last or function for very long, I was also fearful of them sliding.  He has been using these for months now, and they have been very sturdy and the table does not slide when he bumps into it.  Very pleased.
Rating: 5 stars