I only own the 5 series. This one already came with connecting material.

Yes, this was included (a good rack) :-)

Hello, so if you would take the trouble to read through the description, you wouldn't have to ask such things.

Here is an extract from the description:

The 5-tier shoe rack can be stacked with a Songmics 3-tier shoe rack to create 8 tiers using the supplied connectors, increasing the storage space for men's and women's shoes.

So the answer is yes