Overall length 3.8". Drilled for control radius of 1.737" (44.13mm), 1.5" (38mm) and 1.25" (36.75mm). Threaded for 3mm fasteners. Your ball joints made for 3mm or 4-40 bolts through the balls can be installed on this servo arm with 3mm fasteners. Horn fits on splines then clamps with tightening of two fasteners requiring a 2mm socket head wrench. No horn to spline slop is possible with this horn. SKU Number: RRCAA3.5JR