Nickel blank plantchet?

I found this in a coin star today. It weighs 4.9 grams. Sounds just like a nickel when it hits a hard surface. I am wondering if this is a blank plantchet. If not could someone teach me what to look for? Like weights and measurements

 

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well actually I know that it's nothing because I took it to a magnet and it was magnetic so it's steal not nickel. Thought for sure it might be it but still would be nice to know all the specifics

 

elc box pop out.

 

Searcher64 got it right, It is what is called a Knock-out plug from an electrical juction box.