I would put in a vote for TI rounds here (JR344). As flexible and supple as the flats, smooth to the touch like the flats (don't know how they do that with rounds), but with all the growl you could wish for.
Sliding harmonics are a doddle.
Some chorus and reverb (not too much) and a slight boost to the mids = Harmonic Heaven.
Bought from Shepster on here, who was at the end of his Ampeg phase.
Apparently, I'm at the beginning of mine, and this pedal was an excellent starter.
In excellent condition, and £30 gets it posted to your UK doorstep...
I think these are Rotosounds. The ball ends suggest D'Addario? I stand to be corrected...
Don't know the gauge or construction either! They do play nicely, though. Cut for a 4 inline headstock.
Very little use, as I prefer flats.
A tenner gets them posted to your door.
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