Alternate vent system includes Vent gear motor, drive shaft, rail vent rack and pinion, shaft supporter, wheel supporter, handspike,supporting wheel,rack and pinion connectors etc ... greenhouse air circulation could be maximized duet to alternate vent system. NameModelSpecificationAlternate Vent PinionCLJC-1---Alternate Vent RackCLJC-1050L=1050 mmALternate ...