Some of the Parts returned by LIST PARTS will be of type Decoupler. It is a type of Part, and therefore can use all the suffixes of Part. It serves as base for all decouplers, separators, launch clamps and docking ports. Alias Separator can also be used for Decoupler.

structure Decoupler
Suffix Type Description
All suffixes of Part   A Decoupler is a kind of Part
structure Separator

Separator is an alias for the structure Decoupler