3-in Double Side Alum Adjustable Spline Servo Arm: JR/Air This is the JR Radio 3-inch Double Side Adjustable Spline Servo Arm.Features:Silver coloredMade of polished aluminumFirst ever from JR RadiosAdjustable splines make it easier than ever to fit onto your favorite servoNote: Holes are tapped for 4-40 thread screws for use with 4-40 HD Ball Links by Hangar 9 (HAN3616) or other HD 4-40 ball links