Twbydy-am-by-3 -

(since it says "piece" in the prompt): "TRI" or "TRIO" ? But length 3 → "TRI" .

(Roman numeral for 3, "piece" as in a piece of a set). twbydy-am-by-3

Given typical puzzle answer lengths, is a clue for "AM" with something? No. (since it says "piece" in the prompt): "TRI" or "TRIO"

Given the cryptic style, I suspect ; "am" = morning = "AM"; "by" = next to; "3" = three letters; total maybe "FOUR AM" → anagram? "am" = morning = "AM"

But without more context, the cleanest match to a 3-letter "piece" is (as in a piece of something) — but the wordplay "twbydy" doesn't yield that.