There was a note on the lathe that the pulley was broken. It just came apart, i put it back together. It is adjustable groove width/diameter. I don’t know if its the original pulley, but it is probably made to only run in one direction. If the lathe is put in reverse it is more likely to unscrew(widen) and fall apart, or just loosen so that the belt slips and wears it out(so lets keep an eye on it). If it falls apart again, just look at it and you can figure it out: You just screw it back on until the belt is tight, Might have to loosen the set screw. Then tighten the set screw. Could probably put lock-tite on the shaft threads or at least the set-screw. I didn’t do that though.