A slider unit for a tertiary air duct between a clinker cooler and a calciner of a clinker kiln line. The slider unit has at least one shutoff device, which is insertable into a tertiary air duct to seal it without further reducing the cross section of the tertiary air duct, and provides reliable sealing of the tertiary air duct and control of the tertiary air flow, if the slider unit has at least one control device which is insertable into a section of the tertiary air duct to reduce its cross section.