What size/type of nut for LCA Bumper?

Thanks for the reply Mike. No lock washer on the other side. It’s a locking nut. I went to Home Depot and was going to try and see what fits, but their nuts aren’t loose anymore (in baggies). Was just hoping someone knew the thread size.

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Probably 3/8 coarse thread. Slip a 3/8" wrench or socket over the stud to make sure.