This is a sail servo arm that fits on the S3801 servo

FEATURES: black plastic construction

INCLUDES: 1 servo arm

SPECS: 4 7/8" overall length 3 15/16" & 4 1/4" (from center of hole where attaches to servo to the centers of the linkage holes) 7/8" at widest point (where mounts to servo) 3/8" at narrowest point (furthest away from servo) LAS:7/16/95

COMMENTS: THIS FITS ANY FUTABA SERVO, BUT MAY HURT GEARING ON HIGH-TORQUE APPLICATIONS. Since the S125 has a square spline this arms will not fit without an adapter, which we don't carry at this time. UPDATE  

BOX DIMENSIONS: 3.50" W. X .38" H. X 5.38" L. BOX WEIGHT: .03 LBS.