Yes, "Kellem" grips are Hubbell's brand of a "Chinese finger". When sized and used correctly, they won't let go. The key is the length of the grip, not the diameter. Way too often, people spread these things open wider than they should, resulting in less pulling grip. I can take one designed for up to 1/2" and force it onto a piece of 750, but the grip range length is reduced to half of what it should be. THAT's were failures occur.
"But the guy at Home Depot said it would work."