How many letters does the top answer for “mechanical device that has a plunging or thrusting motion” have?

The most common answer is piston (6 letters).

Crossword clue: mechanical device that has a plunging or thrusting motion

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

piston 6 letters wn-def

mechanical device that has a plunging or thrusting motion

plunger 7 letters wn-def

mechanical device that has a plunging or thrusting motion