They were used, as you would expect, on Strat heads with vintage trems: Floyds have retainer bars, Kahlers essentially do the same with the locknut behind the regular nut, and Charvel/Jackson pointy heads didn't need them because the headstock was angled back. Without a string retainer you don't always get the proper string angle over the nut for the high B and E strings. Here is a good pic of Charvel brass string retainers:
http://www.sandimascharvel.com/stringtree.htm
http://www.sandimascharvel.com/stringtree.htm
Comment