This tool at Smith’s Tavern is a wooden mallet, which was used as part of flax processing. The retted flax should be then dry and be crispy for the next steps of breaking and scutching. In breaking, the woody core of the flax steam is broken into crumbs called shives or boon. A flax-brake is used to do this chore, which looks like a large wooden jackknife with a pair of blade-like boards hinged on a grooved base. After breaking, the flax is further cleaned by scutching or swingling. Each bundle is held against a sturdy wooden block and scraped with a dull wooden blade or wooden mallet to strike off any remaining bits of chaff and straw.
Reference: A Weaver’s Garden: Growing Plants for Natural Dyes and Fibers, by Rita Buchanan, pages 26-27.