This is a 19th-century wooden folding shipwright’s rule stamped “J. SMITH’S SHIPWRIGHT’S RULE,” with brass fittings and a distinctive shaped brass head.
Shipwright’s rules were specialized measuring and calculating tools used by shipbuilders and ship carpenters. They typically combined standard inch scales with dedicated timber-measure scales (to calculate the volume of squared timber in cubic feet), board measure, and often proportional lines for determining the diameters of masts, yards, and spars at various points along their length. These specialized scales helped craftsmen who needed quick, practical calculations without complex arithmetic.
Folding rules of this general type appear from the 17th century onward (earlier examples were often single-piece or simpler). By the 19th century, boxwood or other hardwood folding rules with brass hinges, tips, and decorative or protective ends were standard workshop tools. The shaped brass head visible in the photos is a characteristic feature of many period folding rules, providing both a hanging point and protection.
This example is clearly marked as a shipwright’s rule, indicating it was intended for (or sold into) the shipbuilding trade rather than general carpentry. The wood shows the typical darkening, wear, and patina of long workshop use.
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