I ordered a temp sending unit for my 1956 Mercury, the description said for 1956 Ford car but it is the wrong thread. The new sending unit is 3/8 NPT but the hole in the head is 1/4 NPT. I read an old post on here that mentioned that the 1957 is 1/4 NPT.  Can someone please confirm that. If it is, then I will just order a 1957 temp sending unit. I do not want to start using reducers/adapters. Previous owner had installed a mechanical gauge with adapters. I have verified that the gauge in the dash works, so I want to put an original type sending unit back in. I have already installed a mechanical gauge on the front of the engine in the hole for the heater return hose just before the thermostat.
Is the 57 sending unit 1/4 NPT?  If not, what sending unit do I need?
Thank you for any tips.