Based on your inability to properly measure the post, you need to find a friend with a set of calipers and maybe some DIY skills to share. It isn't hard to learn but maybe you need a little help.
You need to fit the lug to the terminal. A too-big lug gives a poor connection, works loose, and can twist and short.
But lugs that are the right size for your wire.
I much prefer crimped and soldered to the ones with little screws.
There are cheap flimsy and low current lugs available in kits at Harbor Freight, Amazon, ebay and other places. Avoid those.
Consider a BFA style banana which is much more foolproof and IMHO gives a better connection.
Jerry