Be very cautious when using steel wool, most wire wools are made of conductive material, very fine metallic residue can find their way to your pick-ups, and could even short them out. If you use it, first tape off your p/u's and make a cover for the rest of the guitar out of poster board, cardboard etc.., the residue is hard on a finish too, use it, clean everything, and then remove the cover, tape etc, those fine little crumbs of wool are extremely hard to get off the pole pieces of a fender p/u, ( don't ask me how I found that out). I like some of the synthetic type pads and wools and even an old piece of leather are great for cleaning fretboards, alot of the syn stuff is made in the 00-0000 range, Cigarette Lighter fluid ( NAPTHA) is a good solvent for using general cleaning, dried snot, blood, body oils etc, off the fretboard, neck and body, just enough to dampen a cloth, sorry no huffing, I use pure lemon oil or carnuba wax to treat rosewood or ebony fretboards, laquer, etc, finished maple fretboards don't need any treatment.B/F, is this thing on your fretboard, down in the finish, sticking up out of the finish, ?