 You drill a hole in the concrete, you push the anchor in, and then when you put your fastener in there, whether it's a screw or a lag bolt or something, you expand the anchor. It forces it out to the sides. And being lead, it's softer and it conforms to the texture of the inside of that hole within the concrete. And they bite in and they tighten up. I mean, they're cheap and they're easy and the bolts or screws can be removed easily.