A coupling for the handle shaft of a flailing line type trimmer which permits angular adjustment of a drive head. The coupling clamps two parts of the handle shaft together. The coupling prevents rotation of one part and permits the selectible rotation of the other. It is preferably formed as a split clamp joining and securely holding the parts in abutment. A pin on the split clamp engages a recess in the end of one handle shaft part to prevent its rotation while a lip on the split clamp engages a circumferential groove in the other handle shaft part to enable it to rotate. A releasable fastener permits loosening of the clamp to allow rotational adjustment of the parts, and their retention at a selected orientation.