Plugging Threaded Hole and Locking Thread

For the plug, I'd look first at www.caplugs.com

Loc-tite 222 sounds good for what you want. I assume the thread diameter is fairly small and you need only moderate strength? Loc-tite has really good technical sales; you might want to talk with them. They've always been helpful to me even when I wanted to do something odd.

You might consider using safety wire to secure that thumbscrew against vibration. If you employ a threadlocker, you will have to apply it every time you twist the screw. Granted, you will have to cut or loosen the safety wire, but you won't have to remove the screw to replace it. Safety wire is put into use by drilling a hole in the thumbscrew, running wire through the hole, and securing the wire to a near, stationary object. As an aircraft electronic technician in the USAF, I used many yards of wire to secure fasteners.

A stainless steel set screw or pipe plug is a excellent weather resistant plug.The compound below is not bad and is not hard to remove.Just squirt it in.

As for the thread locker.I have often used the common silicone gasket/caulking compounds for such as you are asking about for many years now.It does not have to be replaced each time.I have been very familiar with the use of it and many of the Loctite products since 1963.Now both surfaces must be VERY CLEAN before application.Alfred

ps.please forgive the heavy black letters.My spell check does this and I do not know how to correct it.I spent my life working with tools.Computers give me a fit.

You could use a patch-lock screw. Alternatively you could buy or make a screw with a nylon locking insert. You would need to cross drill or blind drill the threaded part of the screw & insert a nylon slug. All of these are re-usable.