This is the Du-Bro Micro Servo Arm XL Set. At last, servo arms long enough to provide the extra throw needed on the electric 3D airplanes! Includes four single arms, as well as two 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" from the center to the outer edge. The Micro Servo Arm XL comes in (4) different versions to accommodate various micro servos on the market. Compatible with Bluebird 303, 306, 308 and 371 as well as MPI MX-30 servos.