This is an anodized aluminum servo horn for the Power HD Ultra-High-Torque, High-Voltage Digital Giant Servo HD-1235MG. The HD-1235 ships with a set of plastic horns, but metal is the way to go if you want to get the most torque out of this 1/4-scale servo.
This metal servo horn is an optional accessory for the Power HD’s HD-1235MG giant servo. For ultra-high-torque applications, this anodized aluminum horn makes a much more robust lever arm than the plastic horns included with the HD-1235MG servo.
This dimension diagram is also available as a downloadable pdf (79k pdf).