A steam distributing coil is a lot like a standard steam coil. The major difference is in its tube-in-tube design. The interior tubes distribute steam through orifices along the tube. This allows the steam to be better spread out, and helps to prevent freezing. For that reason, they are given the nickname Non-freeze -- but, they certainly can freeze, especially if freeze protection is not considered.
Steam Coils come in a variety of shapes and sizes, but there are some properties that are common in most steam coils:
Steam coils operate at the highest temperatures of any other common coil type. As such, only 1-2 rows are usually required.
Larger tube diameters are common for steam distributing coils. 5/8" to 1-1/8" are all common sizes -- with 1" normally preferred for appropriate condensate drainage.
Connections for Steam coils are typically MPT (Male Pipe Thread) and made from copper. Typically the steam inlet diameter is larger than the outlet by at least 1 size.