Compatible with Sti FS38 FS45 FS46 FS55 and FS55R series trimmers and brushcutters. Throttle trigger for ergonomic engine speed control and on/off operation. Direct replacement for Sti part number 4140-180-1500 and equivalent trigger assemblies. Ensures reliable throttle response and comfortable operation during extended use. Facilitates handlebar control system repair and maintenance on homeowner and professional-grade trimmers.