Du-Bro Micro Servo Arm XL (Grey) Part No: 931. AT LAST, servo arms long enough for the extra throw needed on the electric 3D airplanes! The Du-Bro Micro Servo Arm XL includes (4) single arms, as well as (2) double arms. These arms have had extra special attention given to weight, strength and performance. Made from 100% virgin nylon, they can stand up to the stress of 3D aerobatics and still remain lightweight. The arms measure 1" (25.4 mm) from the center to the outer edge. This version works for the following servos: JR 241, JR281, Spektrum DS 821.