An end-effector assembly comprising a master boom, a crossbar coupled to the master boom, at least one branch rail, and a swing arm is provided. The at least one branch rail is movably coupled to the crossbar by a branch lock. The at least one branch rail has a driving groove formed longitudinally therealong for telescopic movement relative to the crossbar. The branch lock comprises a crossbar clamp and a branch rail clamp. The crossbar clamp is slidably and pivotally disposed about the crossbar for slidable and pivotal movement therealong. The branch rail clamp comprises a body having a primary telescoping lock including a receiving bore formed therethrough and a wedging collet disposed in the receiving bore. The body further comprises a secondary telescoping lock having a ball and a plunger disposed in a ball-plunger cavity of the body.