This universal jar opener is an ergonomically engineered assistive tool designed to restore independence to elderly individuals and those living with arthritis. Utilizing a modular dowel-and-hole system, the design allows for rapid adjustment to fit a wide variety of lid diameters, while the 6.6-inch handle leverages mechanical torque to minimize the physical force required from the user. Every dimension was mathematically validated using the Flexure Formula to ensure a Factor of Safety of 3.2, guaranteeing that the 3D-printable PLA structure can easily withstand daily functional stresses. This project represents the first of a five-part series of open-source, easy-to-produce designs aimed at solving common mobility and fine-motor challenges through accessible engineering and human-centered design.