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A few years ago I got 2 dozens of these to secure roof base plate on top of concrete column.. but after we put in the lag shields.. we couldn't insert the main screws so we didn't add the extra screws and the structural engineer was not even sure how to use this.

Now I'll use these to attach a breaker panel to a concrete wall. I need to know. Are these only used on soft cement like hollow blocks so the lag shield can expand against the cement.. or can you really use this for pure concrete.. but how could the lag shield expand against the very hard concrete surrounding it?

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Traditionally, those were made of lead. They didn't so much expand as squish outward against the concrete, engaging with it on a micro level.

These newer pot metal ones can be a pain. They aren't really intended to expand much either, but because they're so hard it's difficult to drive the screw in. You just have to get rowdy with your wrench. It may also help to run the drill bit in and out a few times to make sure you have a fully round hole with no debris left inside.

If you find that you're breaking screws off you may want to try another brand or type of anchor.

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I have used thousands of these of all sizes in all kinds of concrete, there should be no difference in hard or soft concrete, the concrete is not supposed to compress or anything like that.

Make sure that the drill bit is the exact right size for the shields you are using, and try to use screws and anchors from the same brand.

Blow the debris out of the hole before inserting the shield, the dust may effectively make the hole smaller. It should not take much force to insert the shield.

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