When you say "new sensor" do you mean cossie inlet air temp sensor? (I'm assuming so as you show a cossie coolant sensor in the pic as you mentioned) If so, the cossie IAT sensor is M14x1.5
(the ECT sensor that you show is M12x1.5mm)

Are you sure the original is M16? IIRC I thought they were 3/8" BSP..?
When we fitted cossie temp. sensors to the zetec inlet (same original sensor thread as EFi AFAIK) i used a 3/8"x1/4" reducing bush, drilling the bore out and tapping M14x1.5 for the sensor - this leaves very little wall thickness! so use Loctite threadlock and screw the adaptor bush in carefully, then when it's set, screw in the sensor.

If it's not the cossie IAT sensor you are trying to fit, then I'll get my coat..