[156T1978A]: These time switch trippers suitable for T100 Series. [Package Contains]: 2 gold trip units, 2 silver trip unit and 4 fixing screws(a total of 8 trip units and 8 fixing screws). [For T100 series]: Please use 1 silver ON trip unit with J letter and 1 gold OFF trip unit.For all other models: Please use 1 silver ON trip unit and 1 gold OFF tripper. [Compatibility]: T100 series, 1A219, 1A220, 1A573, 1A850, 2A208, 2A209, 2EO21, 2EO22, 2EO23, 2EO25, 2E214, 2E214, 2E25, 2E25, 2E25, 3E25, 35E3, 4EO24, 4EO25, 4EO26, 6X757, 6X759, 6X760, 6X767, 6X768 and 6X769. Also fit Intermatic time clocks - T101, T102, T103, T104 and 102-20, 104-20, T104M, T104R, T101M, T101R. [Easy to install]: Loosen the fixing screw on the trip unit, slide the trip unit to the timer dial for on/off action at the required time, and tighten the fixing screw. Make sure that the correct time is under the current time pointe 156T1978A