From your description and the historical context, it sounds like what you found at the yard sale might be a manual laundry wringer or possibly an antique washboard.

Here's how they were used:
Washboard: A washboard is a wooden or metal board with ridges that was used for scrubbing clothes by hand. It helped loosen dirt and stains when combined with soap and water.
Manual Wringer: A wringer consisted of two rollers turned by a hand crank. After clothes were washed and rinsed, they would be fed through the wringer to squeeze out excess water, making the drying process faster.
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