This is the Sail Servo Arm for the Hitec HS-815BB Servo, HRCM3183. FEATURES: White plastic construction INCLUDES: One servo arm REQUIRES: Installation onto the servo SPECS: Length: 4.89"(124mm) Distance from center servo mounting hole to 1st hole: 3-15/16"(100mm) Distance from center servo mounting hole to 2nd hole: 4-1/5"(108mm) Width at widest point: 7/8"(22mm) Width at narrowest point: .40"(10mm) jxs 02/08/07 ir/jxs