Signal Block Naming Conventions

Usually, the name of the signal block indicates the data type. A signal block ending in _f indicates that the block will input or output a float (depending on its function). A signal block ending in _fc, indicates that the block will input a float and output a complex. Sometimes, a block may end in a _vff, indicating that the input and output are a vector of floats. You can assume: _b for byte, _s for short, _i for int... and so on.

Keep in mind, not all signal block names follow this suit. Some blocks input or output a particular data type, but do not specify this in the name. Ex: audio.sink always takes a stream of floats but does not end in _f.
Other blocks do not expect a specific input or output type. In these cases, you must specify the size of the data type (in bytes) as one of the signal block's parameters. Ex: gr.null_sink can take a stream of any data type, but the first parameter must be the size of the data type in bytes.

Source : Josh Knows