I have noticed this small button hole on the bottom of many scopes and don't know what it's for. I bought this used Primary Arms 3-18x50 scope online, always knowing what you get may not be the best, but I took my chances since it was a decent deal. On the bottom, it appears the small screw or plug that goes in the hole was put in crooked and then grinded down. What are these holes for, and is there a certain tool I can use to get this taken out and put back correctly?

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