rubber hammer
other.— «“Rubber Hammer”—Another imaginary tool a green horn is sometimes sent for.» —“Trade Jargon—Carpet Industry” by Ellis H. Custer in Westchester and Yonkers, N.Y. Lexicon of Trade Jargon Mar. 23, 1938. (source: Double-Tongued Dictionary)
Further reading
What if, instead of being an inanimate object, a dictionary were alive? That’s the idea behind a lavishly illustrated new children’s book called The Dictionary Story (Bookshop|Amazon) by Oliver Jeffers and Sam Winston. This is part of a...