Smart-T is for use with DDB or NDB only. It allows multiple light strings to be connected to a single output port.
It is waterproof and has 1 male and 2 female 3-pin connectors. The 8" Smart-T is about 8" across and the 12" Smart-T is about 12" across. Both have a 3" drop cable.
There is a hook on top for hanging in the open.
It can also be hidden from view by mounting it above a panel, with only the center drop wire hanging down through a hole (0.725 inch diameter). It works well with panels about 0.1 inches thick.