Something like this? Polishing Kit
https://www.thomann.at/intl/musicnomad_fret_polishing_kit_mn124.htm
What’s with the different gauges for the fret rubbers? Is this from rough to smooth?
https://www.thomann.at/intl/hosco_h_fpr_set_polishing_rubbers.htm
I can’t see those links for some reason, but fro,m the links in the description they sound right. These are the sort of thing I use …
Applying excessive downward force onto the string into the frets; rather than a smooth upward motion is probably a main one. Couple that with repeated practice, particularly in one spot, and you’re generating alot of excessive heat and friction. Slightly uneven or seldom polished frets will factor in also
