It's pretty a standard thread size of 1/4"-20 which is a course thread.  I believe this is the standard thread for tripod/camera/scope mounts too.
http://www.homedepot.com/p/Everbilt...-Nuts-4-Pack-54454/202105592?N=5yc1vZc2elZ402
As far as a ball head, again I think it is overkill.  Think of it this way, when using a tripod, the "platform" is essentially fixed.  If you mounted a scope or binoculars straight to the tripod, the only way to change the view would be to actually move the tripod.  This is where a pan or ball head is needed to allow you to easily change the view without having to pick up and move the tripod.
Now, with a trekking pole, you essentially have a monopod.  Think about those photographers you see on the sidelines of a football game.  They don't need any sort of head because they can just rotate the monopod to change the view.  Need to look up, tilt it back.  Need to look down, tilt it forward.  You are always going to have at least one hand on it to steady and aim it.  You can also adjust the height to further assist in looking up or down.
Lenses are mounted directly to the monopod
Leaning forward to look down
Now, here is a lady that is using some sort of head on a monopod.
Overall, I'm not saying that it won't work, I just think it might be more than you really need.  I would suggest getting to a camera shop and seeing if you can try out a monopod with your binoculars to see if you would really need a head.  Who knows, maybe you find a setup that really works slick so be sure to come back and give us a report.