Not supposed to be there. If its threaded, can only imagine that somebody drilled/tapped it to use as a mounting point for some type of bracket.
Not going to speculate what the bracket might have been for, you’ll have to ask the guy that drilled/tapped it.
Hope this helps.
Best,
PM T2
He's livin' in his own private Idaho..... I hope to go out quietly in my sleep, like my grand-dad did..... and not screaming, like the passengers in his car...
Just my humble opinion. If it’s an 1/8th pipe thread maybe a previous owner had a primer cup threaded in there.
My 29 Chief doesn’t have a hole either.