[HELP] Name of this strange T-fitting where one branch is much smaller

[tancredi1970]

What do you term/name this type of T-fitting where one branch is smaller:

In this installation with a T-fitting, one branch is to the cistern, and one branch to an aftermarket non-electric bidet seat.

But - one branch is of much smaller diameter than the regular size.

What do you call this type of T-fiitting? The left branch (white flexible hose) is around 0.3 in/8 mm and the braided (regular)
branch is around 0.6 in/15 mm.

Thank you.

 

[JG plumbing]

I call it a double outlet stop. I'm not actually sure the proper name. But if you say double stop, or two outlet stop, or double outlet stop, a plumber or supply house should know what you mean.