This Re-Fill bottle is designed to refuel our String Fuel Applicator Part Number MN109 (sold separately) once the applicator becomes dry over a period of time due to usage. Our String Fuel formulation is a hybrid blend of refined naturally occurring oils that are speed blended with premium quality mineral oils to deliver a string cleaner & lubricant like no other. Our proprietary formulation allows you to both clean & protect your strings to last longer & sound better while reducing the finger noise & enhancing the speed you can slide your fingers. It's silicone free & even conditions unfinished fretboard wood. This bottle can re-fuel the String Fuel Applicator (sold separately) a minimum two times.