The phrase "of a piece" is an expression that refers to something that's consistent in its character or quality. There are several synonyms that you can use instead of this phrase to convey the same meaning. For instance, you can use the phrase "uniform" to describe something that's consistent or homogeneous, or the term "homogeneous" itself can express the lack of variety. Likewise, you can use the term "identical" or "alike" to describe something with no difference or distinction. Other synonyms for this phrase may include "consistent," "compatible," or "harmonious." In essence, there are numerous words that you can use in place of "of a piece," depending on the context and intended meaning.