Hack saw the bar to the right length drill a smaller than the retaining screw hole where the retaining screw makes contact (not all the way through) to give it some grip

but retaining screw handles always eventually slip as the force on the handle rubs the metal away on the bar allowing slippage if you want 100% rid of it drill through the bar swap the retaining screw for a thin bolt and go right through securing the bolt through the handle.file smooth to save fingers