Anyone know what this type of hardware is called? Trying to

Mounting plate?

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>>373850
That sounds familiar

>>373813
>how it's made without custom engineering.

That looks like a variation of a stud joint. Those are usually welded joints where the arc is created between two workpieces and then cooled down while still in an assembly jig.

You could make a baseplate like that, drill holes, thread the holes and screw a piece of a threaded rod in so it pokes out a bit. Weld the poking out end with the plate.

Things get more hairy if that's a critical component and needs also to be annealed and tempered. You can still make it like that but now you need an access to heat treatment equipment too. Also you need materials that can be heat treated.