The Stillson wrench was designed and patented by Daniel Stillson in 1869. Since then, the design of the wrench hasn’t changed much, even after being produced by countless tool manufacturers. Old Stillson wrenches, also known as “pipe wrenches” and “monkey wrenches,” can be worth a significant sum due to their age and how they reflect the craftsmanship of the era. These wrenches don’t have a lot of information stamped on them to narrow down exact production dates, but you can approximate the age of a wrench to within a few years based on a few clues.
Locate the name of the manufacturer on the Stillson wrench itself, usually near the head or handle. If the company is still in business, browse the company’s product catalog to see if the wrench is still in production. If the company is no longer in business, research the company’s years of operation to narrow down the wrench’s age.
Locate the patent date at the top of the Stillson wrench near the company name. This date will help approximate the age of the wrench by showing the year the device was patented.
Locate a five- to seven-digit patent number at the top of the wrench. Cross-reference the patent number using the U.S. Patent and Trademark Office’s patent database. In most cases, this will produce a patent date that can be used to determine the wrench’s age.
Consult an antiques dealer or a historian specializing in antique tools. The antiques dealer or historian may be able to determine the approximate age of the wrench by using clues that are left unnoticed by untrained eyes.