"the threaded hole "
The problem I've found with threaded holes is that it is hard to see them unless the lighting is just right.
Did you mean, maybe, a nut? A hexagonal piece of metal with a threaded hole in the middle of it?
Your picture is so tiny I can't be sure of what you mean, but it looks like you have circled one of the contact posts, and those are just nuts and bolts designed so the power connections can be firmly bolted on to the solenoid. It looks like there's a nut on the post (bolt) and normally the battery cable ends in a "lug" terminal. You remove the nut from the post, slide the lug terminal over the post, and then put the nut back on.
For some perverse reason we call this "bolting down" the cable, even though it is the nut we are turning.
DO BE SURE the battery positive post is disconnected before you work on any of this. If it tool arcs out a battery cable while you are working--you can literally blow a finger off from the arc, or set the boat on fire, among other ways to ruin your day.