What do you think the hole is for in the middle of this hose splitter?

What do you think the hole is for in the middle of this hose splitter?
<https://www.walmart.com/ip/Orbit-Brass-Hose-Y-for-Faucet-Watering-Shut-Off-Garden-Hose-Splitter-58249/199284331>

That hole is in a bunch of different hose splitters - but not all of them.
<https://www.homedepot.com/p/Morvat-Brass-Garden-Hose-Splitter-Heavy-Duty-2-Way-Hose-Connector-Fitting-MOR-BCONNECTOR-2-A/316286197>

It's also in this brass hose splitter:
<https://www.homedepot.com/p/Heavy-Duty-Brass-2-Way-Y-Valve-3-4-in-Garden-Hose-Splitter-with-Shutoff-2-Hose-Washers-and-Comfort-Grips-3-4-inch-2482/320876424>

And it's in this long hose splitter which is of a completely different design.
<https://www.homedepot.com/p/Morvat-Brass-Garden-Hose-Splitter-Heavy-Duty-4-Way-Hose-Connector-Fitting-MOR-BCONNECTOR-4-A/316480236>

Yet, it's not in this hose splitter:
<https://www.homedepot.com/p/Heavy-Duty-Brass-2-Way-Y-Valve-Connector-Hose-Splitter-without-Shutoff-2-Hose-Washer-3-4-inch-2499/320876511>

It's even in the schematic diagrams, so it's intentional.
But they never say what it's there for.

Why?