The K-21 is distinguished from the more common K-22 by a colon after the G of 128.G and also before the G or GEORGIA. It is an incredibly rare Guide Book type, with fewer than 10 examples thought to exist.

The Bechtler family headed by Alt Christoph, his two sons August and Karl, and nephew Christoph arrived from Pforzheim in Baden, first to New York then Philadelphia where they opened a watch repair shop in Philadelphia. Accomplished gunsmiths and watchmakers, likely well aware of the large quantities of gold coming from the Southern Appalachian Mountains, the Bechtlers picked up and headed to Rutherford County, North Carolina in March or April 1830. Beginning sometime in July of 1831, Christopher Bechtler, as Alt Christoph had become known, set up his own assay office and private mint just north of town. The family started out coining $2.50 and $5 coins, all very utilitarian in design, then later they also introduced the nation's first gold dollar, beating out the United States Mint by about 17 years.

The fineness of the gold coming to the Bechtler's mint varied widely depending on where it was mined. GEORGIA came to mean the finest gold at roughly 22 carats, CAROLINA at 21 carats, and finally N. CAROLINA at 20 carats. The Bechtlers created and modified dies depending on the purity and weight, and in so doing creating a wide variety of different coin types. The federal government got into the act in 1838 and established branch mints near the gold-producing regions at Charlotte and Dahlonega, which impacted the Bechtlers' minting operations. Health issues along with a penchant for overindulging in alcohol led to a decline in business and finally sometime around 1849 or 1850 Christopher Jr. shut the coining business down in its entirety. The Bechtler coins were heavily used throughout the Southern states for many years afterwards. The Georgia-marked pieces at their higher purity level were especially in demand, which also meant they suffered from wear as well as later meltings. The Mint actively tried to pull any examples of Bechtler's coins out of circulation and used them for their own products, leaving behind only a comparative few for today's collectors to enjoy.

The example to the left was sold by Stack's Bowers Galleries in the August 2020 Collectors Choice Online Auction, where it realized $78,000.