Its possible to keep a machine screw from loosening by first degreasing or cleaning the threads, and then coating them with oil paint, your choice of color. With the paint still wet, assemble and tighten to whatever position you desire. The paint will dry, and help keep the screw in place. However, paint will not stand up to repeated movement of the screw, it will gradually wear off. So, this is not a permanent solution, it will just get you by for a while.

I'm not familiar with your folk harp....like Eric said, eventually whatever you put on will wear off in the long run.
How often do you turn?
I'm thinking of silicone, you can experiment on some other screw first and see.
The screw goes into a nut right??...I'm thinking of a nylon lock nut, these can hold fairly long.
What I have done in the past,...drilled a small hole true the nut and pushed in a nylon pin tight, this pin will
rub against the thread, thus creating friction and nut staying put.

Or something what has tension, ...the screw could be split in that section where the mating part goes.
Splitting in half with a very fine slitting saw about half thickness of a hacksaw, [machine shop] this section then
slightly spread open, this makes tension, ... perhaps the nut could be cut open one side too and pushed together slightly what creates tension.

Konrad

Thanks for the information. The problem I'm having is a bit different than what I first thought. The metal pin that holds the string end is tapered and fits into a tapered hole in hardwood. From other forums I learned my problem is common. I will try the oil paint suggestion first.

Harps are tuned often, daily or more. On my folk harps I usually tune a couple times during practice. Tuning is a huge issue because harpists spend so much time tuning. From other forums I read that designing and installing the tuning mechanisms is challenging. My harp maker has changed mechanisms since my harp was built.

An irony is that I traded in a harp with the same, though more severe, problem, because it had slowly progressed to being impossible to tune.

Since the threads are tapered, it's a little more complicated. I wonder if you could use PFTE thread tape, like plumbers use, or pipe dope?

Is the tapered hole directly in the hardwood, or is there a metal insert? Unless there's technical reasons for it being done that way, it sounds as if the way harps are made hasn't changed for centuries.

If you could afford to, and there was no technical reason not to, the ultimate answer would be a metal insert that was threaded inside, which would give you more durability.

There is also an automotive product called a "helicoil" which is a very durable stainless steel spring-like product which replaces worn-out threads and becomes the new thread itself. A tapered thread might not be possible with helicoil, your best bet is an epoxy glue type thread repair such as:

Here is a link that might be useful: Permatex stripped thread repair

Hm...perhaps Teflon..I would give it a try.

Konrad

Here is a link that might be useful: Teflon Tape

Yes teflon is the right choice.

Here is a link that might be useful: concrete bolt

lol:)

The metal pin that holds the string end is tapered and fits into a tapered hole in hardwood. Yea, I suspect it's been this way for centuries.

Teflon tape sounds like a good try! I'll report back.
Thanks!