Found this in an old US Patent Book. Do you know what kind of lock this would operate?
US Patent Key Blank No. 1,977,189 operated an early high security mortise cylinder. I do not know if it ever was manufactured or sold. The curvature of the key matched the cylinder and was designed to deter picking attempts. The notch in the bottom of the key near the tip operated a secondary locking mechanism that effectively worked like a modern sidebar. There was a third locking mechanism near the bottom front of the cylinder which prevented the plug from turning without the bottom pins being at the shear line. There was also a hardened ring between the second and third chamber to prevent a drilling attack. The slope at the tip of the key actually operated the pin in the sixth chamber. The plug also had a bi-level shear line with the first two chambers being elevated higher than the last four chambers. I imagine that duplicating that key would be a challenge, and rekeying the cylinder would be an all day project.
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