It is a very simple component but can significantly help tuning stability. They provide the correct amount of tension where the strings break over the nut.
Stratocaster/Telecaster Compatible String Tree Retainer 5.0mm High
Roller String Tree Retainers (1pair) Compatible with Strat Tele
2X Guitar String Tree Roller Guide Tree String Retainer Electric Stratocaster
Reverend Triple Tree - Guitar String Tree
Electric Guitar Roller String Tree Retainer String Guide Chrome Black Gold
Electric Guitar String Retainer Tension Bar Floyd Rose Black String Tree 45/48mm
