Abstract: A relay comprising an electromagnetic coil wound on an insulating bobbin, the central cavity of which encloses a central spring-biased contact actuated by a magnetic armature in response to energization of the coil, to make or break contact with one or more fixed contacts also enclosed. A U-shaped member and a heel plate, both of highly magnetically permeable material, surround the coil and complete the magnetic circuit for flux generated by the coil. The magnetic armature is constructed and arranged such that it is accessible from the exterior of the enclosed relay to adjust the position of the spring-biased contact of the relay after it is assembled to conform with the desired level of voltage required to actuate the relay.