The aluminium base profile around the bottom of the Greenhouse is 118mm tall and unless modified needs to be stepped over to go in and out. This Low Door Threshold kit allows the base to be reduced to only 40mm height (approximately). This option is only suitable where you will be sitting the base on a solid surface like a concrete strip or slab and is only needed for sliding door entrances (as hinged door entrances have a low threshold included). This size suits a double door entrance, for a single door entrance you just cut the threshold to size.