[skydiverlv]

The print indicates the tie down to be drilled and tapped at both top and bottom.
I would like to know if the top machining is necessary? If so, what goes in the upper one during assembly?

 

[Geico266]

The upper end is tapped to allow for a tie down on the top of the wing if you need to secure the wing after removal, say tie down in a trailer. There is a hole in the top skin over the hole that you can enlarge to access the threaded hole if you need to, or just put a rivet in it and close it up. It's optional.