The Floyd Rose Original String Retainer is used to angle the strings down so they contact the whole surface of the locking nut. If there is not enough headstock angle and the strings aren't flat against the locking nut surface they will go sharp as the locking nut is tightened and pulls the strings down, correcting this with the fine tuners uses up some of their range for later adjustments. The bar has a round bottom and slight radius to minimise friction on the strings.