you have two options:
a) get an adapter off kando ebay m12x1.25 - 1/8 and use thread sealant as the adapter doesnt have that much room for the sensor probe it will stick out a tad
b) what i have is a r31 ecu coolant sensor which is m12x1.5, use a m12x1.25 die to make it suit and wire it up . works great