The holes in this cut off switch are made for 3/8" bolts.
Installation: Remove your negative battery cable, install the disconnect on the negative battery terminal with the bolt provided and then re-attach the vehicle's cable to the threaded terminal of the disconnect. To break the connection from the vehicle to the battery just unscrew the knob until it loosens up. It would be a good idea to open a door-etc to confirm that the battery is unhooked from the vehicle (no lights come on-etc.) Wear safety glasses during the install.