I bought 10 of these. They’re really good. And cheap! Much stronger than my pony or magnum brand ones.
https://www.acklandsgrainger.com/en/product/SPRING-CLAMP-METAL-6-IN/p/WSWCS6M
https://www.acklandsgrainger.com/en/product/SPRING-CLAMP-METAL-6-IN/p/WSWCS6M