Balboa 2" heater split nut
This is the 2-part nut for the union found on either end of a Balboa 2" heater/control box. It has an assymetric 2" FBT thread. Since it comes in two pieces, there is no need to cut out your existing pipework to make the repair.
The nut, like the rest of the union (see list below), is made of white ABS plastic.
Inside diameter at the thread: 75 mm
Inside diameter at the exit: 58 mm
Thickness: 34 mm