There are only 11 slats for a Double bed and the slat separators have provision for 12 slats. There is enough room within your bed for the slat separators and leave the empty slot at the foot end of the bed as per the picture below:

Single beds will not require a centre beam nor cross beams. The slat seperators only will be supplied and used for these beds. There are only 11 slats for a Single bed and the slat separators have provision for 12 slats. The empty slat should be at the foot end of the bed as per the image below.