These work just fine for the purpose (holding a tablecloth in wind), but they're not as strong as alternatives.

As a craftsman, I need slightly stronger clamps since I use them to hold my business sign in place as well (not too heavy, and really just leaning in place). I like that the clamps are red (to fit my tablecloth), which was hard to find. I ended up buying clamps from Home Depot (also red), which twist down to clamp very securely. 4 stars