This is the Gear Set from Hitec. This works on the Hitec HS-45HB Servo (HRCM0987).

FEATURES: Black karbonite construction Karbonite is a material stronger than plastic

INCLUDES: Complete gear set for the HS-45HB servo

REQUIRES: Installation on the servo

COMMENTS: Instructions are not included  

BOX DIMENSIONS: 2.75" W. X .50" H. X 3.00" L. BOX WEIGHT: .01 LBS.