NOTE: If you should accidentally drill the holes too large for your threaded harp pins and the don't fit - you can install tapered harp pins. You'll need to ream out the holes with a #5 tapered reamer.
It's a tuning pin! It's threaded! (And that's good.)
Seriously, it's a threaded tuning pin. Good quality, exactly as described. I've ordered these twice - three to replace the tapered cello-style pegs (What a pain to tune with!) on my symphonie and twenty-five to replace the bog-standard tapered pins on my Witcher Trondheim harp. (I used the D-sized bit, also from Musicmakers, for both applications.)
For the symphonie, I had to drill another string hole through the key-end of the shaft on one of the tuning pins; slowly with a good bit and some cutting oil, it worked fine.
These are much better than tapered tuning pins. If you're building or restoring a harp (or symphonie!) you should consider using these.
Note 1: Initial installation takes longer than for tapered pins, because each pin must be screwed into the hole, rather than just press-fit. The fine threads require thirty to fifty rotations, depending on the thickness of the wood. I used a ratchet with a 5.5mm 12-pt socket.
Note 2: The (kind of scary) statement on the product page (at this writing) that if you make a mistake, you can ream the hole for a tapered pin makes little sense to me. The tapered pin holes on the Trondheim were *smaller* than the D-sized drill bit used for these threaded pins. (Granted, this is a singular datum, but there it is.) Plus, there are ways to deal with an oversized hole, from shims to fill-and-redrill.