A terminal device is described which is attachable to the end of a prosthesis on an arm and there serves as an attachment site for a variety of tools or implements designed to mate with the terminal device. A locking ring mechanism is also described herein. The terminal device comprises a first main part in operable and pivotal combination with a second main part, the combined main parts providing on one end a device for attaching to the end of an a prosthesis, and on the other a device for attaching a variety of implements, the said device for implement attachment providing articulation capabilities that allow positioning of the implements in a variety of positions relative to the position of the arm prosthesis. Among the implements which can be attached are for example: cutting tools (such as saws, files, knives, scrapers, and awls); various wrenches (such as open end wrenches, closed end wrenches, ratchet wrenches, adjustable wrenches, Allen wrenches, and pipe wrenches); and a variety of other implements such as spoons, scoops, spatulas, planes, brushes, sports equipment (e.g., fishing rods), and stirring devices.