Sturdy aluminum construction (violet in color). Single sided arm with 3 pre-drilled M2 starter holes on each arm Splined mounting hole for easy repositioning Designed to fit JR/Graupner standard size servos with approx. 6mm output shaft. Many larger (1/4 scale) servos have approx. 7-1/2mm shaft. The holes in M2, Length 27 mm.