Abstract: A plate lock system for use with cylinder slots having inwardly-angled slot walls. The system includes at least one lead clamp assembly having at least one lead clamp positioned adjacent at least one inwardly-angled slot wall, at least one trail clamp assembly having at least one trail clamp, and at least one register assembly having at least one register. At least one of the lead clamp assembly, the trail clamp assembly and the register assembly is a modular assembly having moving parts that are assembled together in a manner that allows limited relative movement between the moving parts. The modular assembly can be installed into the print cylinder slot through the slot opening without disassembling the moving parts. Also provided are printing plate clamp assemblies, a printing plate lock systems, and printing plate register assemblies.