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The phrase "balls to the wall," sounds as if it is a reference to a part of the male anatomy, which causes some confusion as to what it originally meant. However, the original usage has nothing to do with anatomy, but came rather from military aviation.

On an airplane, the handles controlling the throttle and the fuel mixture are often topped with ball-shaped grips, referred to by pilots as "balls." Pushing the balls forward, close to the front wall of the cockpit results in the highest possible speed.

This phrase is often thought to have come from railroad work, but there is no evidence to support that story. No use of the phrase is known to exist prior to the mid-1960s, and all the early cites are from military aviation.