“Not sure what this is, but the patent dates to 1863. It’s an unusual brass gauge, numbered 1–12. One side reads ‘Roston,’ the other seems to say W Hall. There’s a 38 at the top and a small pin on the side that lets the center flip or move. Any thoughts?”

The mechanism itself is surprisingly elegant. Each tab contains a small internal notch, and only when all notches are perfectly aligned can the internal bolt slide open. A side pin applies tension, making even one misaligned tab enough to keep the lock closed. With no springs or gears involved, the design relies purely on accuracy and craftsmanship. Handling the lock reveals a tactile feedback, allowing the user to sense when the correct alignment is near.

Because of its unusual appearance, the lock is often mistaken for a measuring instrument or mechanical tool. Once its function is understood, however, the design becomes clear and remarkably efficient. Today, collectors value this lock for its durability, historical context, and mechanical ingenuity. More than 150 years later, many examples still function smoothly, serving as a reminder that thoughtful design and quality materials can stand the test of time without needing embellishment or replacement.