What size Random flow generator do i need

[Freshermenreefer]

I have a 3 g tank i want some random flow but i dont understand what RFG i need it got a number 2 on the one in the picture that come with the tank

 

[Biglew11]

That looks like it should be 3/4.

 

[vetteguy53081]

It should thread right in unless 1/2” is needed

 

[Freshermenreefer]

That looks like it should be 3/4.

Thank u so a size 3/4