An implement is connectable to the lifting hitch of a tractor and at least one rotary tool is driven to rotate about an upwardly extending axis. The tool or a trestle frame has an overload connection that allows the tool or frame to pivot to an inoperative position upon overload. The tool can be a blade on a carrier part that is pivoted to a support part on a spoke and a shear pin interconnected to prevent such pivoting unless tripped by overload. The parts can have a discharge arrangement that ejects the sheared pin portion from a recess in one part. Upon adjustment of the tool, the pin remainder can effect reconnection. In another embodiment, the trestle frame is coupled to a three point hitch and the implement can be tripped through a pivot connection, including a strut made up of two shaft parts, one of which holds a shear pin and the other receives a pin portion near the junction of the parts. The pin element normally prevents relative pivoting of the implement relative to the tractor connection. Upon overload the strut jack-knifes to allow the entire implement to pivot relative to the trestle.