Banana plugs are used to carry DC and low-frequency signals. Power Supplies to multimeters typically use banana plugs. Standard banana plugs may only be used for less than 33 V, since they have exposed metal parts. Engineers and technicians often use banana jacks on custom fixtures, early prototypes, or informal “one-off” projects. Sheathed banana plugs are rated for use with higher voltages, and are used for multimeter test leads.