This is the Hitec Standard Metal Servo Horn.

Features

Single arm style constructed of blue anodized aluminum with four
pre-drilled linkage holes.
Fits Hitec servos that have a "+" stamped on top of the output shaft
or any brand servo with a 5.5mm diameter output shaft.

Includes

One Hitec Standard Metal Servo Horn

Requires

Attaching to output shaft with phillips screw (not included).

Specifications

Length from center: 0.87" (22mm)
Thickness: 0.08" (2mm)
Diameter of center hole: 0.22" (5.5mm)